Mapping Charge Recombination and the Effect of Point Defect Insertion in Gallium Arsenide Nanowire Heterojunctions

TL;DR

This study uses advanced STEM EBIC imaging to map and manipulate electronic defects in GaAs nanowire heterojunctions, revealing how surface and point defects influence charge collection efficiency and device performance.

Contribution

It demonstrates the ability to non-destructively map and intentionally introduce point defects in GaAs nanowires, linking defect location to changes in charge recombination and efficiency.

Findings

Surface defects limit charge collection efficiency.

High-energy STEM introduces vacancy-interstitial defects.

Single defect insertion reduces efficiency by approximately 10%.

Abstract

Electronic devices are extremely sensitive to defects in their constituent semiconductors, but locating electronic point defects in bulk semiconductors has previously been impossible. Here we apply scanning transmission electron microscopy (STEM) electron beam-induced current (EBIC) imaging to map electronic defects in a GaAs nanowire Schottky diode. Imaging with a non-damaging 80 or 200 kV STEM acceleration potential reveals a minority-carrier diffusion length that decreases near the surface of the hexagonal nanowire, thereby demonstrating that the device's charge collection efficiency (CCE) is limited by surface defects. Imaging with a 300 keV STEM beam introduces vacancy-interstitial (VI, or Frenkel) defects in the GaAs that increase carrier recombination and reduce the CCE of the diode. We create, locate, and characterize a single insertion event, determining that a defect inserted 7 nm from the Schottky interface broadly reduces the CCE by 10% across the entire nanowire device. Variable-energy STEM EBIC imaging thus allows both benign mapping and pinpoint modification of a device's e-h recombination landscape, enabling controlled experiments that illuminate the impact of both extended (1D and 2D) and point (0D) defects on semiconductor device performance.