Abstract
The impact ionization characteristics of (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> P have been studied comprehensively across the full composition range. Electron and hole impact ionization coefficients ( α and β, respectively) have been extracted from avalanche multiplication and excess noise data for seven different compositions and compared to those of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As. While both α and β initially decrease gradually with increasing bandgap, a sharp decrease in β occurs in (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> P when x > 0.61, while α decreases only slightly. α and β decrease minimally with further increases in x and the breakdown voltage saturates. This behavior is broadly similar to that seen in Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As, suggesting that it may be related to the details of the conduction band structure as it becomes increasingly indirect in both alloy systems.
Highlights
I MPACT ionization is the mechanism of carrier generation in semiconductors that are responsible for the internal gain of avalanche photodiodes (APDs)
The dark currents for all samples were less than 1 nA at up to 95% of breakdown voltage (Vbd) as shown in Fig. 1 due to the wide bandgaps of these alloys
It has been observed that the ionization coefficients decrease with increasing aluminum concentration, resulting in an increase in Vbd with increasing aluminum content
Summary
I MPACT ionization is the mechanism of carrier generation in semiconductors that are responsible for the internal gain of avalanche photodiodes (APDs) It is the cause of avalanche breakdown, which is a failure mechanism in many electronic devices that are subject to a high electric field. It is important that the characterization of semiconductor materials includes accurate knowledge of the electron and hole impact ionization coefficients, referred to as α and β, respectively. These parameters are defined as the reciprocal of the mean distance that a carrier travels between ionization events at a given electric field.
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