This article reports a multi-gain-stage avalanche photodiode based on InGaAs/InAlAs superlattice, which has much higher gain and signal-to-noise ratio than conventional APD. The physical mechanism of high gain and low noise of this type of APD is analyzed in detail, and the dead space gain theory (DSMT) is introduced and applied to the calculation of the excess noise factor of multi-gain-stage APD. For a 5-stage device, the distribution of electric field and carrier dead space is calculated, and the ionization rates before and after considering phonon scattering are compared. The gain vs excess noise factor curve is obtained and compared with the traditional McIntyre model. The simulation results shows that the excess noise factor is equivalent to the McIntyre model k=0.049. Based on the simulation results, an optimized epitaxial material structure is designed, Front-illuminated photo diode were etched in the molecular beam epitaxy (MBE)-grown epitaxial material, the mesa sidewalls were encapsulated with Si3N4 . The test results of a 50μm diameter device are as follows: maximum above 1000, excess noise factor of 2.39@M=100, spectral response range of 0.95~1.65μm, response time of 1.26ns.
The simulations of quasi one-dimensional (1D) and quasi three-dimensional (3D) device process and optoelectronic performance were conducted on silicon APD array pixels using Silvaco, realizing micro region analysis of the electric field distribution, avalanche gain, and photoelectric response characteristics of the APD photosensitive region. The multiplication coefficients corresponding to different positions of APD pixel were obtained and compared with the ideal 1D device structure. The results show that the multiplication factor of the center region of APD pixel is significantly higher than that of the edge of the photosensitive region. The simulation of microlens to converge the incident light to the center of the photosensitive region confirmed the increasement of APD avalanche multiplication current, i.e. the quasi 3D structural APD response is increased from 13.6 A/W to 54.8 A/W, and the effective fill factor is increased from 20.9% to 84.2%. Thus, the utilization rate of incident light is effectively improved.
Based on the fact that laser detectors need to be stored for long time but used only once, the research on main stress and acceleration model, which affect storage life was performed. First, design principles for safe accelerated range of stress, stress forcing method and test time for accelerated test were presented, and the way to estimate the type of life distribution. Then, the method of accelerated model parameter evaluation based on maximum likelihood estimation (MLE) were proposed to calculate the accelerated factor. Finally, based on the accelerated factor, the test data was conversed for evaluation of storage life. The research of the paper can be used as a reference for products of the same type to evaluate the storage life.
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