Govt. Exams
Entrance Exams
In photoconductive (reverse-bias) mode, the depletion region widens significantly, reducing junction capacitance and transit time, resulting in faster response (MHz to GHz range) and shot noise is suppressed due to the reverse field.
The depletion width W = √(2εε₀(V_bi + V_R)/(eN_D N_A/(N_D + N_A))) depends on applied voltage, doping concentrations, and built-in potential. Both doping levels and reverse bias voltage are critical factors.
Maximum power point (MPP) occurs where P = V × I is maximum, typically at ~80% of V_oc and ~80% of I_sc, determined by the fill factor.
The wavelength of emitted light λ = hc/E_g, where E_g is the bandgap. Different materials (GaAs, GaN, AlGaAs) emit different colors based on their bandgap energy.
GaAs has electron mobility ~8500 cm²/Vs compared to Si (~1350 cm²/Vs), making it superior for high-frequency and high-speed applications.
Transconductance g_m = ∂I_D/∂V_GS measures how much the drain current changes with gate voltage, a key figure of merit in MOSFET amplifier design.
In saturation, the MOSFET acts as a voltage-controlled current source with I_D proportional to (V_GS - V_T)^2, independent of V_DS beyond saturation voltage.
Higher substrate doping increases the surface potential needed to invert the channel, raising V_T. This is described by V_T = V_T0 + γ(√(2φ_f + V_SB) - √(2φ_f)).
In active mode, the BE junction is forward biased to inject carriers, while the BC junction is reverse biased to collect these carriers, ensuring transistor amplification.
I_s is the reverse saturation current, representing the leakage current when the junction is reverse biased. It depends on temperature and doping concentrations.
