AI Lect 6 Fall 2024/2025 Semiconductors and Diodes PDF

Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes...

Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Ch.4: Semiconductors and diodes Lect.6: Semiconductors and diodes 6.1 Semiconductors *Semiconductors are a special class of elements having a conductivity between that of a good conductor and that of an insulator. *Semiconductor materials fall into one of two classes: single-crystal and compound. * Single-crystal semiconductors such as germanium (Ge) and silicon (Si) have a repetitive crystal structure. *Compound semiconductors such as gallium arsenide (GaAs), cadmium sulfide (CdS), gallium nitride (GaN), and gallium arsenide phosphide (GaAsP) are constructed of two or more semiconductor materials of different atomic structures. The three semiconductors used most frequently in the construction of electronic devices are Ge, Si, and GaAs. Germanium (Ge) is used with diode (year 1939) and transistor (year 1947) Germanium was used almost exclusively because :- -It was relatively easy to find and was available in fairly large quantities. -It was also relatively easy to refine to obtain very high levels of purity, an important aspect in the fabrication process. -Also it was discovered in the early years that diodes and transistors constructed using germanium as the base material. Germanium suffered from low levels of reliability due primarily to its sensitivity to changes in temperature. Silicon, had improved temperature sensitivities, but the refining process for manufacturing silicon of very high levels of purity was still in the development stages. The first silicon transistor was introduced in 1954. Silicon quickly became the semiconductor material of choice:- -Not only is silicon less temperature sensitive, -but it is one of the most abundant materials on earth, removing any concerns about availability. Si transistor networks for most applications were cheaper to manufacture and had the advantage of highly efficient design strategies. The field of electronics became increasingly sensitive to issues of speed. Computers were operating at higher and higher speeds, and communication systems were operating at higher levels of performance. A semiconductor material capable of meeting these new needs had to be found. The result was the development of the first GaAs transistor in the early 1970s. GaAs transistor had speeds of operation up to five times that of Si. (Lect.6) Page 1 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul GaAs was more difficult to manufacture at high levels of purity, was more expensive, and had little design support in the early years of development. However, in time the demand for increased speed resulted in more funding for GaAs research, to the point that today it is often used as the base material for new high-speed, very large scale integrated (VLSI) circuit designs To fully appreciate why Si, Ge, and GaAs are the semiconductors of choice for the electronics industry requires some understanding of the atomic structure of each and how the atoms are bound together to form a crystalline structure. The fundamental components of an atom are the electron, proton, and neutron. In the lattice structure, neutrons and protons form the nucleus and electrons appear in fixed orbits around the nucleus. The Bohr model for the three materials is provided in Fig.5.1. FIG. 6.1 Atomic structure of (a) silicon; (b) germanium; and(c) gallium and arsenic. Table 6.1 Orbiting electrons for some semiconductors Semiconductor Silicon Germanium Gallium Arsenic tetravalent tetravalent trivalent pentavalent Orbiting electrons 14 32 31 33 Electrons in outermost shell (valance electrons) 4 4 3 5 6.1.1 Covalent Bonding and Intrinsic Materials Electrons in the outermost shell is named valence electrons Intrinsic silicon material has 1.5*1010 free carriers in 1 cm3 at room temperature intrinsic carriers are the free electrons in a material due only to external causes Relative mobility (μn ) of the free carriers in the material, that is, the ability of the free carriers to move throughout the material From Table 6.2, Ge has the highest number and GaAs the lowest. Ge has more than twice the number as GaAs. (Lect.6) Page 2 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul The number of carriers in the intrinsic (ni) form and the relative mobility (μn ) are more significant in determining its use in the field. Comparison between Si , Ge and GaAs are indicated in Table 6.2 Table 6.2 Intrinsic Carriers ni semiconductor Intrinsic carriers / cm3 relative mobility (μn ) (Cm2 / V s) (indicate response time) GaAs 1.7*106 8500 Si 1.5*1010 1500 Ge 2.5*1013 3900 One of the most important technological advances of recent decades has been the ability to produce semiconductor materials of very high purity. Recall that this was one of the problems The ability to change the characteristics of a material through this process is called doping , something that germanium, silicon, and gallium arsenide readily and easily accept. One important and interesting difference between semiconductors and conductors is their reaction to the application of heat. Conductor has positive temperature coefficient ( i.e. resistance increases with temperature). Semiconductor has negative temperature coefficient ( i.e. resistance decreases with temperature). Semiconductor materials have a negative temperature coefficient. 6.1.3 n -Type and p -Type Materials The characteristics of a semiconductor material can be altered significantly by the addition of specific impurity atoms to the relatively pure semiconductor material. These impurities, although only added at 1 part in 10 million, can alter the band structure sufficiently to totally change the electrical properties of the material. A semiconductor material that has been subjected to the doping process is called an extrinsic material. There are two extrinsic materials (n -type and p -type materials). n -Type Material An n -type material is created by introducing impurity elements that have five valence electrons ( pentavalent). The effect of such impurity elements is indicated in Fig. 6.5 (using antimony as the impurity in a silicon base). (Lect.6) Page 3 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul FIG. 5.5 Antimony impurity in n-type material. Note that the four covalent bonds are still present. There is, however, an additional fifth electron due to the impurity atom, which is unassociated with any particular covalent bond. This remaining electron, loosely bound to its parent (antimony) atom, is relatively free to move within the newly formed n -type material. Since the inserted impurity atom has donated a relatively “free” electron to the structure: Diffused impurities with five valence electrons are called donor atoms. At room temperature in an intrinsic Si material there is about one free electron for every 1012 atoms. If the dosage level is 1 in 10 million (107 ), the ratio 1012 /107 = 105 indicates that the carrier concentration has increased by a ratio of 100,000:1. p -Type Material The p -type material is formed by doping a pure germanium or silicon crystal with impurity atoms having three valence electrons. The elements most frequently used for this purpose are boron, gallium, and indium. The effect of one of these elements, boron, on a base of silicon is indicated in Fig.5.7. FIG. 6.7 Boron impurity in p-type material. Note that there is now an insufficient number of electrons to complete the covalent bonds of the newly formed lattice. The resulting vacancy is called a hole and is represented by a small circle or a plus sign, indicating the absence of a negative charge. Since the resulting vacancy will readily accept a free electron: The diffused impurities with three valence electrons are called acceptor atoms. The resulting p -type material is electrically neutral, for the same reasons described for the n - type material. (Lect.6) Page 4 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Majority and Minority Carriers In the intrinsic state, the number of free electrons in Ge or Si is due only to those few electrons in the valence band that have acquired sufficient energy from thermal or light sources to break the covalent bond or to the few impurities that could not be removed. The vacancies left behind in the covalent bonding structure represent our very limited supply of holes. In an n -type material, the number of holes has not changed significantly from this intrinsic level. The net result, therefore, is that the number of electrons far outweighs the number of holes. For this reason: In an n-type material ( Fig.6.8a ) the electron is called the majority carrier and the hole the minority carrier. For the p -type material the number of holes far outweighs the number of electrons, as shown in Fig. 6.8b. In a p-type material( Fig.6.8b ) the hole is the majority carrier and the electron is the minority carrier. FIG. 6.8(a) n-type material; (b) p-type material. When the fifth electron of a donor atom leaves the parent atom, the atom remaining acquires a net positive charge: hence the plus sign in the donor-ion representation. For similar reasons, the minus sign appears in the acceptor ion. The n - and p -type materials represent the basic building blocks of semiconductor devices. (Lect.6) Page 5 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul 6.2 p-n junction - Diode Now that both n - and p -type materials are available, we can construct our first solid-state electronic device (The semiconductor diode) , with applications too numerous to mention, is created by simply joining an n -type and a p -type material together, nothing more, just the joining of one material with a majority carrier of electrons to one with a majority carrier of holes. The basic simplicity of its construction simply reinforces the importance of the development of this solid-state era. At the instant the two materials are “joined” the electrons and the holes in the region of the junction will combine, resulting in a lack of free carriers in the region near the junction, as shown in Fig. 5.9a. Note in Fig. 5.9a that the only particles displayed in this region are the positive and the negative ions remaining once the free carriers have been absorbed. FIG. 6.9 A p–n junction with no external bias: (a) an internal distribution of charge; (b) a diode symbol, with the defined polarity and the current direction; (c) demonstration that the net carrier flow is zero at the external terminal of the device when V D=0V. This region of uncovered positive and negative ions is called the depletion region due to the “depletion” of free carriers in the region. If leads are connected to the ends of each material, a two-terminal device results, as shown in Figs. 6.9a and 5.9b. Three options then become available: no bias , forward bias , and reverse bias. The term bias refers to the application of an external voltage across the two terminals of the device to extract a response. No bias The condition shown in Figs.6.9a and 6.9b is the no-bias situation because there is no external voltage applied. In Fig..9b the symbol for a semiconductor diode is provided to show its correspondence with the p –n junction. In each figure it is clear that the applied voltage is 0 V (no bias) and the resulting current is 0 A, much like an isolated resistor. The absence of a voltage across a resistor results in zero current through it. Even at this early point in the discussion it is important to note the polarity of the voltage across the diode in Fig. 6.12b and the direction given to the current. In the absence of an applied bias across a semiconductor diode, the net flow of charge in one direction is zero. In other words, the current under no-bias conditions is zero, as shown in Figs. 6.9a and 6.9b. (Lect.6) Page 6 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Reverse-Bias Condition ( VD < 0 V) If an external potential of V volts is applied across the p –n junction such that the positive terminal is connected to the n -type material and the negative terminal is connected to the p - type material as shown in Fig. 6.10 , the number of uncovered positive ions in the depletion region of the n -type material will increase due to the large number of free electrons drawn to the positive potential of the applied voltage. For similar reasons, the number of uncovered negative ions will increase in the p -type material. The net effect, therefore, is a widening of the depletion region. This widening of the depletion region will establish too great a barrier for the majority carriers to overcome, effectively reducing the majority carrier flow to zero, as shown in Fig. 6.10a. The current that exists under reverse-bias conditions is called the reverse saturation current and is represented by Is. FIG. 6.10 Reverse-biased p–n junction: (a) internal distribution of charge underreverse-bias conditions; (b) reverse-bias polarity and direction of reversesaturation current. The reverse saturation current is seldom more than a few microamperes and typically in nA, except for high-power devices. (The term saturation comes from the fact that it reaches its maximum level quickly and does not change significantly with increases in the reverse-bias potential). The reverse-biased conditions are depicted in Fig. 6.10b for the diode symbol and p –n junction. Note, in particular, that the direction of Is is against the arrow of the symbol. Note also that the negative side of the applied voltage is connected to the p -type material and the positive side to the n -type material, Forward-Bias Condition ( VD > 0 V) A forward-bias or “on” condition is established by applying the positive potential to the p - type material and the negative potential to the n -type material as shown in Fig. 6.11. The application of a forward-bias potential VD will “pressure” electrons in the n -type material and holes in the p -type material to recombine with the ions near the boundary and reduce the width of the depletion region as shown in Fig. 6.11a. The resulting minority- carrier flow of electrons from the p -type material to the n -type material (and of holes from (Lect.6) Page 7 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul the n -type material to the p -type material) has not changed in magnitude (since the conduction level is controlled primarily by the limited number of impurities in the material), but the reduction in the width of the depletion region has resulted in a heavy majority flow across the junction. FIG. 6.11 Forward-biased p–n junction: (a) internal distribution of charge under forward- biasconditions; (b) forward-bias polarity and direction of resulting current. An electron of the n -type material now “sees” a reduced barrier at the junction due to the reduced depletion region and a strong attraction for the positive potential applied to the p - type material. As the applied bias increases in magnitude, the depletion region will continue to decrease in width until a flood of electrons can pass through the junction. Diode equation It can be demonstrated through the use of solid-state physics that the general characteristics of a semiconductor diode can be defined by the following equation, referred to as Shockley’s equation, for the forward- and reverse-bias regions: ID = Is {EXP(VD /VT ) -1} (A) (6.1) Where Is is the reverse saturation current VD is the applied forward-bias voltage across the diode VT is called the thermal voltage and is determined by VT = k TK / q (V) (6.2) Where k is Boltzmann’s constant =1.38* 10-23 J/K TK is the absolute temperature in kelvins = T+273 , T is the temperature in °C q is the magnitude of electronic charge =1.6*10-19 C Diode characteristic curve (diode I-V curve) Fig.6.12 Note that the vertical scale of Fig.6.12 is measured in milliamperes (although some semiconductor diodes have a vertical scale measured in amperes), and the horizontal scale in (Lect.6) Page 8 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul the forward-bias region has a maximum of 1V. Typically, therefore, the voltage across a forward-biased diode will be less than 1 V. Note also how quickly the current rises beyond the knee of the curve. FIG. 6.12 Silicon semiconductor diode characteristics FIG. 6.13 Comparison of Ge, Si, and GaAs commercial diodes The barrier voltage (VB) {or the hill voltage (Vh) or knee voltage (VK)} is the center of the knee of the curve. VB = 0.3 V (for Ge) , 0.7 V (for Si) and 1.2 V (for GaAs). Initially, Eq. (6.2) with all its defined quantities may appear somewhat complex. However, it will not be used extensively in the analysis to follow. It is simply important at this point to understand the source of the diode characteristics and which factors affect its shape. A plot of Eq. (6.1) with Is = 10 pA is provided in Fig. 6.12 as the dashed line. If we expand Eq. (6.2) into the following form, the contributing component for each region of Fig. 6.12 can be described with increased clarity: ID = Is EXP(VD / VT) - Is (6.3) (Lect.6) Page 9 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul For positive values of VD the first term of the above equation will grow very quickly and totally overpower the effect of the second term. The result is the following equation, which only has positive values and takes on the exponential format e x appearing in Fig. 6.16 : ID = Is EXP{VD / VT) (VD positive) (6.4) For negative values of VD the exponential term drops very quickly below the level of I and the resulting equation for ID is simply ID = -Is (VD negative) (6.5) Note in Fig. 6.12 that for negative values of VD the current is essentially horizontal at the level of -Is. At V= 0 V, Eq. (6.2) becomes ID = Is (e0 - 1) = Is(1 - 1) = 0 mA as confirmed by Fig. 6.12. The sharp change in direction of the curve at VD= 0 V is simply due to the change in current scales from above the axis to below the axis. Note that above the axis the scale is in milliamperes (mA), whereas below the axis it is in picoamperes (pA). Breakdown Region The current in reverse bias, near a mean reverse voltage, the current increases at a very rapid rate. The reverse-bias potential that results in this dramatic change in characteristics is called the breakdown Potential and is given the label VBV (Fig.6.14). FIG. 6.14 Breakdown region. The breakdown voltage of Si diodes (VB Si) , The breakdown voltage of Ge diodes (VB Ge) , The breakdown voltage of GaAs diodes (VB GaAs) , VB GaAs = 110% VB Si = 200 % VB Ge Temperature Effects Temperature can have a marked effect on the characteristics of a semiconductor diode, as demonstrated by the characteristics of a silicon diode shown in Fig. 6.15 : (Lect.6) Page 10 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul In the forward-bias region the characteristics of a silicon diode shift to the left at a rate of 2.5 mV per centigrade degree increase in temperature FIG. 6.15 Variation in Si diode characteristics with temperature change An increase from room temperature (20°C) to 100°C (the boiling point of water) results in a drop of 80 (2.5 mV) = 200 mV, or 0.2 V, which is significant on a graph scaled in tenths of volts. A decrease in temperature has the reverse effect, as also shown in the figure: In the reverse-bias region the reverse current of a silicon diode doubles for every 10°C rise in temperature. GaAs devices are available that work very well in the -200°C to +200°C temperature range, with some having maximum temperatures approaching 400°C. The reverse breakdown voltage of a semiconductor diode will increase or decrease with temperature. However, if the initial breakdown voltage is less than 5 V, the breakdown voltage may actually decrease with temperature. (Lect.6) Page 11 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul 6.3 Diode Equivalent Circuits An equivalent circuit is a combination of elements properly chosen to best represent the actual terminal characteristics of a device or system in a particular operating region. In other words, once the equivalent circuit is defined, the device symbol can be removed from a schematic and the equivalent circuit inserted in its place without severely affecting the actual behavior of the system. The result is often a network that can be solved using traditional circuit analysis techniques. Piecewise-Linear Equivalent Circuit One technique for obtaining an equivalent circuit for a diode is to approximate the characteristics of the device by straight-line segments, as shown in Fig. 6.17. Fig.6.17 The resulting equivalent circuit is called a piecewise-linear equivalent circuit (Fig.5.18). FIG. 6.18 Components of the piecewise-linear equivalent circuit (ON state) The battery VK opposing the conduction direction must appear in the equivalent circuit as shown in Fig. 6.18 Note, for conduction state, applied voltage across the diode (VD) must be greater than threshold battery voltage (VK) When conduction is established the resistance of the diode will be the specified value of rav. The approximate level of rav can usually be determined from a specified operating point on the specification sheet. For instance, for a silicon semiconductor diode, if IF= 10 mA (a forward conduction current for the diode) at VD= 0.8 V, we know that for silicon a shift of 0.7 V is required before the characteristics rise, and we obtain rav = (ΔVd / ΔId) pt. to pt = (0.8 V - 0.7 V) / (10 mA - 0 mA) = 0.1 V / 10 mA = 10 Ω If the characteristics or specification sheet for a diode is not available the resistance r av can be approximated by the ac resistance rd. (Lect.6) Page 12 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Simplified Equivalent Circuit For most applications, the resistance rav is sufficiently small to be ignored in comparison to the other elements of the network. Removing rav from the equivalent circuit is the same as implying that the characteristics of the diode appear as shown in Fig. 6.19. The reduced equivalent circuit appears in the same figure. It states that a forward biased silicon diode in an electronic system under dc conditions has a drop of 0.7 V across it in the conduction state at any level of diode current (within rated values, of course). FIG. 6.19 Simplified equivalent circuit for the silicon semiconductor diode. Ideal Equivalent Circuit In Fig. 6.20a the diode is acting like a closed switch permitting a generous flow of charge in the direction indicated. In Fig. 6.20b the level of current is so small in most cases that it can be approximated as 0 A and represented by an open switch. FIG. 6.20 Ideal semiconductor diode: (a) forwardbiased;(b) reverse-biased. In other words: The semiconductor diode behaves in a manner similar to a mechanical switch in that it can control whether current will flow between its two terminals. However, it is important to also be aware that: The semiconductor diode is different from a mechanical switch in the sense that when the switch is closed it will only permit current to flow in one direction. Now that rav is considered zero ohm and the VK is considered zero. So, the ideal equivalent circuit becomes as shown Fig.6.21. In this case diode acts as a switch (ON in case forward bias and OFF in case reverse bias) (Lect.6) Page 13 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Note , this approximation is often made without a serious loss in accuracy. FIG. 6.21 Ideal diode and its characteristics In industry a popular substitution for the phrase “diode equivalent circuit” is diode model — a model by definition being a representation of an existing device, object, system, and so on. For the application in mind, the significance of the data will usually be self-apparent. If the maximum power or dissipation rating is also provided, it is understood to be equal to the following product: PDmax= VD ID (6.11) Where ID and VD are the diode current and voltage, respectively, at a particular point of operation. Temperature and applied reverse bias are very important factors in designs sensitive to the reverse saturation current. (Lect.6) Page 14 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Solved Examples Example 6.1 At a temperature of 27°C (common temperature for components in an enclosed operating system), determine the thermal voltage VT. Solution: Substituting into Eq. (1.3), we obtain Tk = 273 + 27 = 300 K VT = kTK / q = (1.38 * 10-23 J/K) (300 K) / (1.6 * 10-19 C) = 25.875 mV The thermal voltage will become an important parameter in the analysis to follow in this course. Example 6.2 Using the curves of Fig Example 6c.2: a. Determine the voltage across each diode at a current of 1 mA. b. Repeat for a current of 4 mA. c. Repeat for a current of 30 mA. d. Determine the average value of the diode voltage for the range of currents listed above. e. How do the average values compare to the knee voltages listed in Table 1.3 ? Fig.5c.2 Solution: a. VD (Ge) = 0.2 V, VD (Si) = 0.6 V, VD (GaAs) = 1.1 V b. VD (Ge) = 0.3 V, VD (Si) = 0.7 V, VD (GaAs) = 1.2 V c. VD (Ge) = 0.42 V, VD (Si) = 0.82 V, VD (GaAs) = 1.33 V d. Ge : V av = (0.2 V + 0.3 V + 0.42 V) /3 = 0.307 V Si : V av = (0.6 V + 0.7 V + 0.82 V) /3 = 0.707 V GaAs : V av = (1.1 V + 1.2 V + 1.33 V) /3 = 1.21 V e. Very close correspondence. Ge: 0.307 V vs. 0.3 V, Si: 0.707 V vs. 0.7 V, GaAs: 1.21 V vs. 1.2 V. (Lect.6) Page 15 of 16 Delta University for Science and Technology Basic Electricity and Electronics College of Artificial Intelligence BAS126 Basic Science and Computer Dep. Lect.6: semiconductors and diodes Fall semester 2024/2025 Prepared by ---------- Assoc. Prof. Adel Zaghloul Example 6.3 Determine the dc resistance levels for the diode of Fig. 5c.3 at a. ID = 2 mA (low level) b. ID= 20 mA (high level) c. VD=10 V (reverse-biased) Solution: a. At ID = 2 mA, VD = 0.5 V (from the curve) and RD = VD / ID = 0.5 V / 2 mA = 250 Ω b. At ID _ 20 mA, VD = 0.8 V (from the curve) and RD =VD / ID = 0.8 V / 20 mA = 40 Ω c. At VD=10 V, ID = - Is = - 1μA (from the curve) and RD = VD / ID = 10 V / 1 mA = 10 MΩ FIG. Example 5c.3. (Lect.6) Page 16 of 16