Semiconductor Physics Question & Answers June 25, 2026 By WatElectronics Semiconductor Physics is one of the most important subjects in Electronics and Electrical Engineering, forming the foundation of modern electronic devices such as diodes, transistors, integrated circuits, solar cells, LEDs, laser diodes, sensors, and microprocessors. Understanding semiconductor physics is essential for students pursuing Electronics and Communication Engineering (ECE), Electrical Engineering (EEE), Physics, VLSI Design, Nanotechnology, and Semiconductor Technology. Semiconductors possess electrical properties that lie between conductors and insulators. Their unique behavior arises from concepts such as energy bands, charge carriers, doping, carrier transport mechanisms, and quantum effects. These principles enable engineers to control electrical conductivity and design devices that power today's computers, smartphones, communication systems, automotive electronics, medical equipment, and artificial intelligence hardware. This collection of 150 Multiple Choice Questions (MCQs) has been carefully designed to provide comprehensive coverage of semiconductor physics, ranging from basic concepts to advanced device physics. The questions include conceptual, analytical, application-oriented, and examination-style problems that help learners strengthen their understanding of the subject. The MCQs cover a wide range of topics, including: Energy Band Theory Intrinsic and Extrinsic Semiconductors Doping and Carrier Concentration Electron and Hole Transport Mobility and Conductivity Hall Effect and Hall Coefficient Fermi Level and Fermi-Dirac Statistics Direct and Indirect Bandgap Semiconductors Carrier Generation and Recombination PN Junction Physics Depletion Region and Built-In Potential Forward and Reverse Bias Characteristics Junction Capacitances Zener and Avalanche Breakdown Photoconductivity and Photodetectors LEDs and Laser Diodes Solar Cells and Photovoltaic Effect Wide Bandgap Semiconductors (GaN and SiC) Crystal Structures and Miller Indices Lattice Defects and Carrier Traps Quantum Tunneling and Heterojunctions Quantum Wells and Nanostructures MOS Capacitors and MOSFET Fundamentals CMOS Technology and Modern Semiconductor Devices. Each question is accompanied by a hint, answer, and detailed explanation to promote conceptual learning rather than simple memorization. These MCQs are suitable for university examinations, competitive examinations such as GATE and IES, technical interviews, semiconductor industry recruitment tests, and self-assessment. By working through these questions systematically, students can develop a strong understanding of semiconductor fundamentals and gain confidence in solving both academic and real-world engineering problems. 1). What is the forbidden energy gap in a semiconductor? The energy possessed by free electrons The energy region where no electron states exist The energy of the conduction band The energy required for recombination None Hint 2). Which material is an intrinsic semiconductor? Silicon Germanium doped with phosphorus Silicon doped with boron Gallium arsenide doped with impurities None Hint 3). At absolute zero temperature, a semiconductor behaves like: A conductor An insulator A superconductor A metal None Hint 4). The conductivity of a semiconductor increases with? Decreasing temperature Increasing temperature Constant temperature Pressure only None Hint 5). The majority carriers in an n-type semiconductor are? Holes Electrons Ions Protons None Hint 6). The majority carriers in a p-type semiconductor are? Electrons Holes Neutrons Ions None Hint 7). Silicon belongs to which group of the periodic table? Group III Group IV Group V Group VI None Hint 8). Which impurity is used to obtain n-type silicon? Boron Gallium Indium Phosphorus None Hint 9). Which impurity is commonly used for p-type silicon? Arsenic Antimony Boron Phosphorus None Hint 10). The unit of mobility is? m²/V•s V/m Ω•m C/s None Hint 11). The Fermi level in an intrinsic semiconductor lies? Near conduction band Near valence band At the center of the bandgap Outside the bandgap None Hint 12). The SI unit of conductivity is? Ω•m S/m V/m A/m² None Hint 13). Which semiconductor has the smallest bandgap? Silicon Germanium Gallium Arsenide Diamond None Hint 14). The bandgap of silicon at room temperature is approximately? 0.67 eV 1.1 eV 1.43 eV 5.5 eV None Hint 15). Gallium Arsenide is a? Elemental semiconductor Compound semiconductor Metallic semiconductor Intrinsic conductor None Hint 16). The charge of an electron is? +1.6 × 10⁻¹⁹ C -1.6 × 10⁻¹⁹ C +3.2 × 10⁻¹⁹ C -3.2 × 10⁻¹⁹ C None Hint 17). Which carrier has greater mobility in silicon? Holes Electrons Both equal Depends only on doping None Hint 18). The process of adding impurities to a semiconductor is called? Recombination Ionization Doping Diffusion None Hint 19). In an intrinsic semiconductor? Electron concentration > Hole concentration Hole concentration > Electron concentration Electron concentration = Hole concentration No carriers exist None Hint 20). The valence band is? Completely empty at 0 K Partially filled at 0 K Completely filled at 0 K Above conduction band None Hint 21). Which of the following is a pentavalent impurity? Boron Gallium Indium Arsenic None Hint 22). Recombination means? Generation of carriers Electron-hole annihilation Doping process Crystal formation None Hint 23). Carrier generation increases when? Temperature decreases Temperature increases Bandgap increases greatly Doping decreases None Hint 24). The conduction band consists of? Bound electrons only Free electrons capable of conduction Holes only D) Atomic nucleir None Hint 25). The energy gap of an insulator is generally? Less than 1 eV Around 1 eV Greater than 3 eV Zero None Hint 26). The drift current is caused by? Concentration gradient Electric field Temperature gradient Pressure None Hint 27). Diffusion current is caused by? Electric field only Magnetic field Carrier concentration gradient Pressure difference None Hint 28). Which semiconductor material is widely used in solar cells? Copper Silicon Iron Aluminum None Hint 29). The intrinsic carrier concentration of a semiconductor depends strongly on? Shape Temperature Color Weight None Hint 30). The mobility of charge carriers decreases primarily because of? Crystal perfection Carrier scattering Vacuum conditions Lower resistance None Hint 31). The Hall Effect is used primarily to determine? Bandgap energy Carrier type and concentration Resistivity only Atomic density None Hint 32). The Hall coefficient of an n-type semiconductor is? Positive Negative Zero Infinite None Hint 33). The Hall coefficient of a p-type semiconductor is? Negative Positive Zero Undefined None Hint 34). The Hall voltage is developed? Along the current direction Across the width of the specimen Along the magnetic field direction At the terminals only None Hint 35). Effective mass of an electron in a semiconductor is? Always equal to free electron mass Usually different from free electron mass Zero Infinite None Hint Semiconductor Physics MCQs for Interviews 36). The density of states represents? Number of atoms per unit volume Number of available energy states per unit energy range Carrier velocity distribution Electron mobility None Hint 37). Fermi-Dirac distribution gives? Electron mobility Probability of occupancy of an energy state Conductivity Carrier lifetime None Hint 38). At the Fermi level, the probability of occupancy at room temperature is approximately? 0 0.25 0.5 1 None Hint 39). The Fermi level in an n-type semiconductor shifts toward? Valence band Middle of bandgap Conduction band Outside crystal None Hint 40). The Fermi level in a p-type semiconductor shifts toward? Conduction band Valence band Middle of bandgap Vacuum level None Hint 41). The product of electron and hole concentrations in thermal equilibrium is? Constant for a given temperature Always zero Equal to doping concentration Infinite None Hint 42). Which law is represented by np=ni2np=ni2? Ohm's Law Hall Law Mass Action Law Kirchhoff's Law None Hint 43). In heavily doped semiconductors, the Fermi level may? Move outside the bandgap Remain fixed at center Disappear Become negative None Hint 44). Which semiconductor has a direct bandgap? Silicon Germanium Gallium Arsenide Carbon None Hint 45). Which semiconductor has an indirect bandgap? Gallium Arsenide Silicon Indium Phosphide Gallium Nitride None Hint 46). LEDs are generally made from: Direct bandgap semiconductors Indirect bandgap semiconductors Metals Insulators None Hint 47). The carrier lifetime is defined as? Average time before recombination Time required for doping Mobility measurement duration Transit time across a crystal None Hint 48). Carrier lifetime is usually measured in? Coulombs Seconds Volts Ohms None Hint 49). Increasing recombination rate causes carrier lifetime to? Increase Decrease Remain constant Become infinite None Hint 50). Diffusion length depends on? Carrier lifetime and diffusion coefficient Temperature only Mobility only Doping only None Hint 51). Which parameter measures how fast carriers spread due to concentration gradients? Hall coefficient Diffusion coefficient Mobility ratio Resistivity None Hint 52). Einstein's relation connects? Bandgap and mobility Diffusion coefficient and mobility Lifetime and conductivity Hall coefficient and bandgap None Hint 53). Which quantity increases when donor concentration increases? Hole concentration Electron concentration Bandgap significantly Atomic mass None Hint 54). The conductivity of a semiconductor is? σ=q(nμn+pμp)σ=q(nμn+pμp) σ=IRσ=IR σ=P/Vσ=P/V σ=V/Iσ=V/I None Hint 55). Resistivity is? Directly proportional to conductivity Inversely proportional to conductivity Independent of conductivity Equal to mobility None Hint 56). When temperature increases in an intrinsic semiconductor? Carrier concentration decreases Carrier concentration increases exponentially Conductivity becomes zero Mobility increases indefinitely None Hint 57). Which mechanism dominates current flow in intrinsic semiconductors? Electrons only Holes only Both electrons and holes Ions only None Hint 58). A semiconductor with extremely high impurity concentration is called? Intrinsic semiconductor Degenerate semiconductor Insulator Compound semiconductor None Hint 59). Which carrier generally contributes more to conductivity in n-type silicon? Holes Electrons Both equally Ions None Hint 60). If donor concentration increases by a factor of 10, electron concentration approximately? Decreases by 10 Remains constant Increases by 10 Increases by 100 None Hint 61). A PN junction is formed by joining? Two n-type semiconductors Two p-type semiconductors A p-type and an n-type semiconductor A metal and a semiconductor None Hint 62). The depletion region in a PN junction is also known as? Conducting region Space charge region Metallic region Neutral region None Hint 63). The depletion region is formed due to? Carrier generation Carrier diffusion across the junction Hall effect Magnetic fields None Hint 64). The electric field in the depletion region points from? p-side to n-side n-side to p-side Both directions No electric field exists None Hint 65). The built-in potential of a PN junction opposes? Recombination Diffusion of majority carriers Generation of carriers Hall voltage None Hint 66). Typical built-in voltage of a silicon PN junction at room temperature is approximately? 0.1 V 0.3 V 0.7 V 1.5 V None Hint 67). Typical built-in voltage of a germanium PN junction is approximately? 0.3 V 0.7 V 1.1 V 1.5 V None Hint 68). Under equilibrium conditions, the net current in a PN junction is? Maximum Infinite Zero Negative None Hint 69). Forward bias means? P-side connected to positive terminal and N-side to negative terminal P-side connected to negative terminal and N-side to positive terminal Both terminals grounded No voltage applied None Hint 70). Reverse bias means? P-side positive, N-side negative P-side negative, N-side positive No connection Both terminals positive None Hint 71). Under forward bias, the depletion region width? Increases Becomes infinite Decreases Remains constant None Hint 72). Under reverse bias, the depletion region width? Decreases Remains zero Increases Changes polarity None Hint 73). The current in a forward-biased diode is mainly due to? Majority carriers Minority carriers Ions only Neutrons None Hint 74). Reverse saturation current is mainly caused by? Majority carriers Minority carriers Donor ions Acceptor ions None Hint 75). Reverse saturation current strongly depends on? Color of the semiconductor Temperature Shape of crystal Pressure only None Hint Semiconductor Physics MCQs for Exams 76). The ideal diode equation is? I=IS(eV/ηVT−1)I=IS(eV/ηVT−1) V=IRV=IR P=VIP=VI Q=CVQ=CV None Hint 77). Thermal voltage at room temperature is approximately? 2.6 mV 26 mV 260 mV 2.6 V None Hint 78). Junction capacitance under reverse bias is called? Diffusion capacitance Depletion capacitance Stray capacitance Mutual capacitance None Hint 79). Diffusion capacitance becomes significant during? Reverse bias Zero bias Forward bias Breakdown None Hint 80). Increasing reverse bias causes depletion capacitance to? Increase Decrease Become zero instantly Remain constant None Hint 81). Avalanche breakdown occurs because of? Tunneling effect Impact ionization Recombination Hall effect None Hint 82). Zener breakdown occurs primarily because of? Carrier recombination Tunneling mechanism Diffusion current Hall voltage None Hint 83). Zener breakdown generally occurs in? Lightly doped junctions Moderately doped junctions Heavily doped junctions Intrinsic semiconductors None Hint 84). Avalanche breakdown generally occurs in? Heavily doped junctions Lightly doped junctions Metals only Intrinsic silicon only None Hint 85). Which breakdown mechanism has a negative temperature coefficient? Avalanche breakdown Zener breakdown Hall breakdown Thermal breakdown None Hint 86). Which breakdown mechanism has a positive temperature coefficient? Zener breakdown Avalanche breakdown Tunnel breakdown Diffusion breakdown None Hint 87). The depletion width is greatest under? Strong forward bias Equilibrium Reverse bias Short circuit None Hint 88). A PN junction at equilibrium behaves like? Open circuit for majority carrier flow Short circuit Perfect conductor Metal wire None Hint 89). In a silicon diode, the forward current increases exponentially because: Ohm's law dominates Barrier potential decreases and carrier injection rises rapidly Resistance becomes infinite Mobility becomes zero None Hint 90). Which statement is TRUE at thermal equilibrium in a PN junction? Drift current > Diffusion current Diffusion current > Drift current Drift current = Diffusion current Both currents are zero None Hint 91). Photoconductivity refers to? Conductivity due to pressure Conductivity increase caused by light exposure Conductivity due to magnetic fields Conductivity decrease with temperature None Hint 92). For photoconduction to occur, photon energy must be: Less than bandgap energy Equal to or greater than bandgap energy Always equal to zero Independent of bandgap None Hint 93). A photodiode is generally operated in? Forward bias Reverse bias Zero bias only Breakdown region None Hint 94). The primary function of a photodiode is to convert: Heat into electricity Sound into electricity Light into electrical current Pressure into voltage None Hint 95). Responsivity of a photodetector is measured in? Ω/m A/W V/m² C²/J None Hint 96). The wavelength corresponding to a semiconductor bandgap is determined using? Einstein relation Planck-Einstein relation Ohm's law Hall equation None Hint 97). Light Emitting Diodes (LEDs) operate based on? Avalanche breakdown Carrier recombination Hall effect Thermionic emission None Hint 98). The color of light emitted by an LED depends mainly on? Device size Bandgap energy Package material Operating current only None Hint 99. Which material is widely used for blue LEDs? Germanium Silicon Gallium Nitride (GaN) Copper None Hint 100). Laser diodes differ from LEDs because laser diodes produce? Incoherent light Monochromatic and coherent light Infrared only Thermal radiation None Hint 101). The process responsible for laser action is? Spontaneous emission only Stimulated emission Hall effect Drift current None Hint 102). Population inversion is required in? Solar cells Hall sensors Laser diodes Thermistors None Hint 103). A solar cell converts? Electrical energy to light energy Light energy to electrical energy Mechanical energy to heat Heat to magnetic energy None Hint 104). The photovoltaic effect is the generation of? Heat from light Voltage from incident light Light from voltage Magnetic field from photons None Hint 105). The open-circuit voltage of a solar cell increases with: Bandgap energy Device area only Temperature only Thickness only None Hint 106). Quantum efficiency of a photodetector is? Ratio of generated carriers to incident photons Current divided by resistance Power divided by voltage Electron mobility None Hint 107). Which semiconductor is commonly used in fiber-optic communication photodetectors? Silicon Carbide Indium Gallium Arsenide (InGaAs) Diamond Selenium None Hint 108). The absorption coefficient of a semiconductor indicates: Carrier mobility How strongly light is absorbed Conductivity Hall voltage None Hint 109). Silicon becomes transparent for photons whose energy is: Greater than bandgap energy Equal to bandgap energy Less than bandgap energy Twice the bandgap energy None Hint 110). Silicon Carbide (SiC) is considered a? Narrow bandgap semiconductor Wide bandgap semiconductor Metal Superconductor None Hint Semiconductor Physics MCQs for Interviews 111). One major advantage of SiC devices is: Low thermal conductivity High breakdown voltage capability Very low melting point Zero resistance None Hint 112). Gallium Nitride (GaN) devices are preferred in high-frequency applications because of: High electron mobility and velocity Low bandgap energy High hole concentration only Low thermal stability None Hint 113). Which semiconductor material has the highest electron mobility among the following? Silicon Germanium Gallium Arsenide Silicon Carbide None Hint 114). Compound semiconductors are formed from elements belonging to: Group I only Groups III and V or II and VI Group IV only Noble gases only None Hint 115). Which material is commonly used for high-power RF transistors? Germanium Gallium Nitride (GaN) Copper Glass None Hint 116). A semiconductor's bandgap generally decreases with: Increasing temperature Decreasing temperature Increasing pressure only Doping only None Hint 117). Carrier mobility usually decreases with increasing temperature because? Carrier generation stops Lattice scattering increases Bandgap increases sharply Hall coefficient becomes zero None Hint 118). The transit time of a carrier is? Time required to cross a device region Carrier lifetime Recombination time only Diffusion coefficient Hint: Related to carrier movement. None Hint 119). Semiconductor devices switch faster when carrier transit time is? Large Infinite Small Negative None Hint 120). Which property makes semiconductors unique compared to metals and insulators? Intermediate conductivity that can be controlled Zero resistance Infinite conductivity No charge carriers None Hint 121). Silicon primarily crystallizes in which crystal structure? Body-Centered Cubic (BCC) Face-Centered Cubic (FCC) Diamond Cubic Structure Hexagonal Close Packed (HCP) None Hint 122). The nearest-neighbor bonds in silicon are oriented at approximately? 45° 60° 90° 109.5° None Hint 123). A unit cell is defined as? The smallest repeating crystal structure A single atom A grain boundary A defect region None Hint 124). Miller indices are used to represent? Energy levels Crystal planes and directions Carrier concentration Mobility None Hint 125). Which silicon crystal plane is most commonly used in MOS fabrication? (111) (100) (210) (321) None Hint 126). A vacancy defect refers to: An extra atom in the lattice A missing atom in the lattice An impurity atom A grain boundary None Hint 127). An interstitial defect occurs when? An atom occupies a normal lattice site An atom occupies a position between lattice sites A carrier recombines A junction breaks downc None Hint 128). A dislocation is classified as: Point defect Line defect Surface defect Volume defect None Hint 129). Grain boundaries are examples of? Point defects Line defects Surface defects Carrier traps None Hint 130). Crystal defects generally? Increase mobility indefinitely Scatter charge carriers Eliminate resistance Increase bandgap dramatically None Hint 131). A carrier trap is an energy level that? Accelerates carriers Captures charge carriers temporarily Generates photons only Increases mobility None Hint 132). Deep-level traps are located? Very close to conduction band Very close to valence band Near the middle of the bandgap Outside the semiconductor None Hint 133). Shallow donor levels lie? Near the conduction band Near the valence band Mid-gap Outside the crystal None Hint 134). Shallow acceptor levels lie? Near conduction band Near valence band Mid-gap Vacuum level None Hint 135). Tunneling refers to? Thermal excitation over a barrier Quantum-mechanical penetration through a barrier Carrier diffusion only Carrier recombination None Hint 136). Tunneling probability increases when the barrier becomes: Wider and higher Wider only Narrower and lower Higher only None Hint 137). Which device primarily relies on tunneling? Zener diode Resistor Transformer Thermistor None Hint 138). A heterojunction is formed between: Two identical semiconductors Two different semiconductor materials Two metals A metal and an insulator None Hint 139). An example of a heterojunction is: Si-Si Ge-Ge GaAs-AlGaAs Cu-Al None Hint 140). A quantum well confines carriers in? One dimension Two dimensions Three dimensions No dimensions None Hint 141). Quantum confinement becomes significant when device dimensions approach: Kilometers Centimeters Nanometers Meters None Hint 142). The gate of a MOS capacitor is separated from the semiconductor by: Metal Oxide layer PN junction Air gap None Hint 143). MOS stands for? Metal-Oxide-Semiconductor Metal-Oxide-System Magnetic-Oxide-Semiconductor Metal-Organic-Semiconductor None Hint 144). Applying a positive voltage to the gate of a p-type MOS capacitor tends to: Accumulate holes Repel holes from the surface Destroy the oxide Increase lattice defects None Hint 145). Inversion in a MOS structure occurs when? Majority carriers dominate the surface Minority carriers dominate the surface Oxide breaks down Junction capacitance becomes zero None Hint 146). The conducting channel in an NMOS transistor consists mainly of: Holes Electrons Donor ions Acceptor ions None Hint 147). Threshold voltage of a MOSFET is the gate voltage required to: Destroy oxide Form a strong inversion layer Cause avalanche breakdown Create recombination None Hint 148). CMOS technology uses: Only NMOS transistors Only PMOS transistors Complementary NMOS and PMOS transistors Bipolar transistors only None Hint 149). One major advantage of CMOS technology is: High static power dissipation Low static power consumption Low integration density High leakage current None Hint 150). Which statement best summarizes modern semiconductor physics? Device behavior depends only on conductivity Crystal structure, carrier transport, quantum effects, and material engineering all play important roles Only doping matters Only temperature matters None Hint Time's up
