Govt. Exams
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.
The intrinsic (lightly doped) region in a p-i-n diode extends the depletion width, increasing quantum efficiency for photon absorption and collection. This improves responsivity and frequency response.
Schottky diodes have lower barrier height (typically 0.3-0.5V vs 0.7V for Si), resulting in lower forward voltage. Faster switching due to majority carrier conduction (no minority carrier storage).
Schottky barrier height Φ_B ≈ Φ_M - χ, where Φ_M is metal work function and χ is semiconductor electron affinity. This makes Schottky junctions useful for various applications with tunable barriers.
