Avalanche photodiodes (APD) can amplify the photoelectric signal based on the avalanche multiplication effect of carrier to improve the sensitivity of detection. They have the characteristics of low noise and high gain, so they are suitable for long-distance optical communication. In this work, a multi-stage avalanche photodiode structure with SAGCM (Separated Absorption, Grading, Charge and Multiplication region) is proposed based on Impact Ionization Engineering (I2E). The photocurrent, dark current, electric field, gain and noise characteristics of InGaAs/InAlAs avalanche photodiodes are studied by optimizing the grading layer's thickness and doping concentration. According to the final simulation results, the optimized avalanche photodiodes has low excess noise. At 60 V voltage and 300 K temperature, the noise factor k value (the ratio of impact ionization coefficients) of the five-stage APD is 0.012, and the gain can reach 430.
InAs/GaSb Type II Superlattice (T2SL) has become a highly competitive material for Infrared (IR) detector. We designed a pπMn mid-wavelength infrared detector based on the InAs/GaSb T2SL materials and studied the influence of the detector structural parameters on the dark current density magnitude and the Quantum Efficiency (QE) from the theoretical simulation level. Through the simulation of the detector material and structure, the dark current density characteristics at various doping concentrations, the dark current density characteristics and QE at different superlattice material thicknesses, and the temperature dependence of the dark current level are calculated. The M-structure barrier is inserted in between the π and n layers of the T2SL infrared detector structure, and the overall dark current level can be effectively reduced. Under the condition of 77 K, according to the final simulation data results, the dark current density can achieve 9.46×10-8 A/cm2, and the peak QE can achieve 34.3%.
The sensitive parameters affecting the dark current characteristics are further studied by using InAs/GaSb type II superlattice (T2SL) pBpp structure long wavelength Infrared photodetectors.Generation of recombination (G-R), surface leakage current and tunneling current are the main components of dark current. Using pBpp structure can suppress them effectively, thereby decreasing dark current. Based on the k ∙ p method, the band structure of InAs/GaSb T2SL and InAs/AlSb T2SL can be obtained by solving the 8-band k ∙ p model. We have calculated different doping levels of pBpp detector and different layer thicknesses of pBpp detector. For pBpp device, we consider the dark current for different contact layer doping and different absorber layer doping. We also study the influence of different contact layer thicknesses and different absorber layer thicknesses on dark current. The dark current of pBpp detector is dominant by tunneling current at low temperature, and diffusion is the main limiting mechanism in dark current at high temperature, for barrier layer inhibits generation-recombination contribution. Eventually, the dark current of a pBpp structure has been calculated for versus voltage at 77 K.
Off-plane band structure for triangular and square lattice with non-zero kz component were calculated using Plane Wave
Expansion Method. Both decreasing, finally breaking down of in-plane band gaps and emerging of new off-plane band
gaps were observed with an increasing kz. Kz component dependence of band gap was investigated in both triangular
and square lattice, with varied air hole radius and dielectric constant.
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