Mid-wavelength infrared avalanche photodetector with AlAsSb/GaSb superlattice

In this work, a mid-wavelength infrared separate absorption and multiplication avalanche photodiode (SAM-APD) with 100% cut-off wavelength of ~ 5.0 µm at 200 K grown by molecular beam epitaxy was demonstrated. The InAsSb-based SAM-APD device was designed to have electron dominated avalanche mechanism via the band structure engineered multi-quantum well structure based on AlAsSb/GaSb H-structure superlattice and InAsSb material in the multiplication region. The device exhibits a maximum multiplication gain of 29 at 200 K under -14.7 bias voltage. The maximum multiplication gain value for the MWIR SAM-APD increases from 29 at 200 K to 121 at 150 K. The electron and hole impact ionization coefficients were derived and the large difference between their value was observed. The carrier ionization ratio for the MWIR SAM-APD device was calculated to be ~ 0.097 at 200 K.

A method for EMCCD multiplication gain measurement with comprehensive correction

In order to improve the image quality, it is imperative to conduct the non-uniformity correction of EMCCD, for which the measurement accuracy of the internal electron multiplication gain of each channel is a prerequisite within multi-channel output EMCCD. It is known that the smaller the image standard deviation of each channel, the better the image uniformity, and the closer the calculated multiplier gain is to the real value. In order to minimize the influence of non-uniformity of background between pixels and light response existing in traditional measurement, a comprehensively modified EMCCD multiplication gain measurement is proposed after the working principle of EMCCD is described. The output images of the camera working in the normal CCD mode and EMCCD mode are corrected comprehensively through this method. The experimental results show that after the comprehensive correction, the standard deviation of the output image of each channel within the camera decreases to about one third of the original when the camera works in the normal CCD mode, while it decreases to about one fifth of the original when the camera works in the EMCCD mode, the signal stability is significantly improved, and the measured multiplier gain of each channel is closer to the true value of the detector, which proves the effectiveness of the proposed method.

Mean multiplication gain and excess noise factor of GaN and Al0.45Ga0.55N avalanche photodiodes

In this work, Monte Carlo model is developed to investigate the avalanche characteristics of GaN and Al0.45Ga0.55N avalanche photodiodes (APDs) using random ionization path lengths incorporating dead space effect. The simulation includes the impact ionization coefficients, multiplication gain and excess noise factor for electron- and hole-initiated multiplication with a range of thin multiplication widths. The impact ionization coefficient for GaN is higher than that of Al0.45Ga0.55N. For GaN, electron dominates the impact ionization at high electric field while hole dominate at low electric field whereas Al0.45Ga0.55N has hole dominate the impact ionization at higher field while electron dominate the lower field. In GaN APDs, electron-initiated multiplication is leading the multiplication gain at thinner multiplication widths while hole-initiated multiplication leads for longer widths. However for Al0.45Ga0.55N APDs, hole-initiated multiplication leads the multiplication gain for all multiplication widths simulated. The excess noise of electron-initiated multiplication in GaN APDs increases as multiplication widths increases while the excess noise decreases as the multiplication widths increases for hole-initiated multiplication. As for Al0.45Ga0.55N APDs, the excess noise for hole-initiated multiplication increases when multiplication width increases while the electron-initiated multiplication increases with the same gradient at all multiplication widths.

The Fabrication and Characterization of InAlAs/InGaAs APDs Based on a Mesa-Structure with Polyimide Passivation

This paper presents a novel front-illuminated InAlAs/InGaAs separate absorption, grading, field-control and multiplication (SAGFM) avalanche photodiodes (APDs) with a mesa-structure for high speed response. The electric fields in the InAlAs-multiplication layer and InGaAs-absorption layer enable high multiplication gain and high-speed response thanks to the thickness and concentration of the field-control and multiplication layers. A mesa active region of 45 micrometers was defined using a bromine-based isotropic wet etching solution. The side walls of the mesa were subjected to sulfur treatment before being coated with a thick polyimide layer to reduce current leakage, while lowering capacitance and increasing response speeds. The breakdown voltage (VBR) of the proposed SAGFM APDs was approximately 32 V. Under reverse bias of 0.9 VBR at room temperature, the proposed device achieved dark current of 31.4 nA, capacitance of 0.19 pF and multiplication gain of 9.8. The 3-dB frequency response was 8.97 GHz and the gain-bandwidth product was 88 GHz. A rise time of 42.0 ps was derived from eye-diagrams at 0.9 VBR. There was notable absence of intersymbol-interference and the signals remained error-free at data-rates of up to 12.5 Gbps.

Effect of Multiplication and Absorption Layers Width on Avalanche Multiplication Gain in InGaAs/InP Avalanche Photodiode

The separate absorption, grading, charge, and multiplication (SAGCM) InGaAs/InP avalanche photodiodes (ADPs) are widely used in long distance, high bit rate optical communication system due to their high performance and response to optical fiber wavelength spectrum. In this work, the effect of multiplication layer width (MLW) and absorption layer width (ALW) on APD performance is studied and investigated. Silvaco TCAD software is used as simulation tools to simulate a precise model of InGaAs/InP APD and analyze its, performance under an illuminated condition. As such, three different ALW with various MLW has been simulated while the structure values and material parameters are kept constant. It was found that in the APD with smaller MLW, the distance between the punch-through voltage and the breakdown voltage can be maximized. Therefore, the operation region of APD will be extended. In addition, the multiplication gain is obtained from the photocurrent and primary current by taking the APD collection efficiency effect under the consideration.