Measuring Minority Carrier Diffusion Length Using High-Injection Scanning Photocurrent Microscopy

TL;DR

This paper demonstrates that high-injection scanning photocurrent microscopy (SPCM) can effectively measure minority carrier diffusion lengths in various semiconductors, including lightly doped and intrinsic types, without requiring Schottky contacts.

Contribution

The study introduces a finite-element simulation approach enabling minority diffusion length measurement under high optical excitation, expanding SPCM's applicability beyond previous low-injection limitations.

Findings

High-injection SPCM accurately measures minority diffusion lengths.

Method applicable to doped and intrinsic semiconductors.

Eliminates need for Schottky contacts in testing devices.

Abstract

Scanning photocurrent microscopy (SPCM) has been widely used for characterizing charge transport properties, in particular, the minority carrier diffusion length of semiconductors. However, studying lightly doped or intrinsic semiconductors using SPCM remained challenging. Methods used in previous work required low levels of optical injection, which could not be fulfilled easily in semiconductors with lower carrier concentration. In this work, using finite-element simulation, we show that the minority diffusion length can also be quantified under high optical excitation. Not only being applicable both doped and intrinsic semiconductors, the method also lifted the restriction of implementing a Schottky contact in testing devices -- a condition assumed to be necessary in previous studies. The results significantly expanded the versatility of SPCM in studying a broad spectrum of semiconducting materials with unprecedented flexibility in experimental conditions.