Source Impurity\nContributions and Polarity Inverting\nin the Unintentional Doping of Al<sub><i>x</i></sub>In<sub>1–<i>x</i></sub>As<sub><i>y</i></sub>Sb<sub>1–<i>y&l

Molecular beam epitaxy grown Al<sub><i>x</i></sub>In<sub>1–<i>x</i></sub>As<sub><i>y</i></sub>Sb<sub>1–<i>y</i></sub> digital alloys have\nshown great\npromise as a materials platform for infrared photodetection, including\nthe demonstration of several state-of-the-art III–V avalanche\nphotodiodes. A primary obstacle facing further sensitivity improvements\nto AlInAsSb digital alloy devices is the inconsistent unintentional\ndoping; here we report the first observations of variations in both\nthe polarity and magnitude of the unintentional doping of these materials,\nand demonstrate outgassing procedures to reach serviceable and stable\nunintentional doping levels routinely after campaign onset. Through\na series of experiments conducted over the course of multiple molecular\nbeam epitaxy campaigns, the aluminum source material purity is shown\nto be a primary contributor of the unintentional doping. Group-V source\noutgassing was found to more weakly impact the unintentional background\nconcentration. A transition from <i>p</i>-type to <i>n</i>-type polarity was observed as the aluminum source was\nprogressively outgassed, as well as an order of magnitude reduction\nin the background carrier concentration. Results obtained from secondary\nion mass spectroscopy and other techniques suggest that oxygen- and\ncarbon-related impurities may be the origin of this <i>p</i>-type doping. After group-V outgassing, dark currents in simple pin-type\nhomojunctions were reduced by several orders of magnitude near reverse\nbias breakdown, underscoring the importance of these studies to device\nperformance.