Multiplication and excess noise in AlxGa1−xAs/GaAs multilayer avalanche photodiodes

Abstract

Impact ionization in 1–2.5 μm thick AlxGa1−xAs/GaAs multiple quantum well (MQW) avalanche photodiodes with various barrier and well widths has been investigated in detail. The measured avalanche multiplication suggests that in all cases no enhancement of the ionization coefficients over that of equivalent GaAs is possible. Excess noise measurements on these structures corroborate the multiplication results and show that no enhancement of the ionization coefficient ratio can be obtained in AlxGa1−xAs/GaAs MQWs by virtue of the heterojunction interfaces, irrespective of the number of repeating units. These results suggest that the excess energy gained by carriers crossing the AlxGa1−xAs/GaAs heterojunction interface is negligible and that the lower ionization coefficients of the AlxGa1−xAs results in behavior that is similar to that of a pseudoalloy of the wells and barriers.

Optimization of GaAs/AlGaAs staircase avalanche photodiodes accounting for both electron and hole impact ionization

“…The F (M ) curve for the APD with diameter 200 µm is in agreement with the experimental results for the GaAs/AlGaAs MQW APD with 25 steps in [13]: the noise is much lower than for the p-i-n diode and its behavior is predicted also by the EBHDM (that is calibrated on p-i-n diodes without additional model parameter changes when considering staircase structures). The F (M ) curve for the device with diameter 600 µm, instead, lies very close to the results reported in [14] for a GaAs/AlGaAs MWQ APD with 15 steps and to the experimental results for the GaAs p-i-n diode [9]. Concerning the difference between the results for the devices in [2],…”

“…APDs that have always abrupt heterojunctions between a low (E G1 ) and a high (E G2 ) bandgap material [13,14], in staircase APDs each stage is linearly graded from E G1 to E G2 and the abrupt discontinuity is only between E G2 and E G1 [12]. The staircase enhances electron II over hole II, which offers the possibility to achieve a good trade-off between gain and excess noise [7].…”

Monte Carlo Simulation of Hot Carrier Transport in Heterogeneous Ge/${\rm Al}_{x}{\rm Ga}_{1-x}{\rm As}~(0\leq x\leq 0.8)$ Multilayer Avalanche Photodiodes

“…Similar heterointerface treatments applied to the simulation of GaAs/Al x Ga 1−x As material system were found to produce excellent agreement between with the experimental avalanche multiplication values for GaAs/Al x Ga 1−x As multilayer heterojunctions with various thicknesses [11], [23]. Although no experimental result of the Ge/Al x Ga 1−x As multilayer structures is available in the literature for comparison, the similar heterointerface conditions and approaches validated in the GaAs/AlGaAs multilayer structures simulation ensured the model has the required essential physical parameters included.…”

GaAs/Al0.8Ga0.2As separate absorption and multiplication region x-ray spectroscopic avalanche photodiodes

“…For example, a GaAs/AlxGa1-xAs SAM APD (320 µm × 450 µm active area) was reported to function as an X-ray detector at room temperature, utilising a series of staircase multiplication regions [18]; an energy resolution of 900 eV FWHM at 13.96 keV was reported at an avalanche multiplication of 4.1 at room temperature [18]. More recent work has concentrated on simpler SAM APD structures [43]. For example, a thin (430 nm GaAs absorption layer, 220 nm Al0.8Ga0.2As multiplication layer) GaAs/Al0.8Ga0.2As SAM X-ray APD was reported at room temperature [44]; it had an energy resolution of 1.08 keV FWHM at 5.9 keV, at an avalanche multiplication of 3.5.…”