Direct Observation of Hole Carrier-Density Profiles and Their Light-Induced Manipulation at the Surface ofGe

T Prokscha,Z Salman,K.-H Chow,E Stilp,A Suter

doi:10.1103/physrevapplied.14.014098

T Prokscha, Z Salman + Show 3 more

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https://doi.org/10.1103/physrevapplied.14.014098

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Abstract

We demonstrate that, by using low-energy positive muon ($\mu^+$) spin spectroscopy as a local probe technique, the profiles of free charge carriers can be directly determined in the accumulation/depletion surface regions of p- or n-type Ge wafers. The detection of free holes is accomplished by measuring the effect of the interaction of the free carriers with the $\mu^+$ probe spin on the observable muon spin polarization. By tuning the energy of the low-energy $\mu^+$ between 1 keV and 20 keV the near-surface region between 10 nm and 160 nm is probed. We find hole carrier depletion and electron accumulation in all samples with doping concentrations up to the $10^{17}$ cm$^{-3}$ range, which is opposite to the properties of cleaved Ge surfaces. By illumination with light the hole carrier density in the depletion zone can be manipulated in a controlled way. Depending on the used light wavelength $\lambda$ this change can be persistent ($\lambda = 405, 457$ nm) or non-persistent ($\lambda = 635$ nm) at temperatures $< 270$ K. This difference is attributed to the different kinetic energies of the photo-electrons. Photo-electrons generated by red light do not have sufficient energy to overcome a potential barrier at the surface to be trapped in empty surface acceptor states. Compared to standard macroscopic transport measurements our contact-less local probe technique offers the possibility of measuring carrier depth profiles and manipulation directly. Our approach may provide important microscopic information on a nanometer scale in semiconductor device studies.

Highlights

The characterization of semiconductor materials and devices is key for understanding and developing semiconductor technologies
By using low-energy positive muon (μ+) spin spectroscopy as a local probe technique, the profiles of free charge carriers can be directly determined in the accumulation-depletion surface regions of p- or n-type Ge wafers
We directly explore by means of low energy μSR (LE-μSR) the hole depletion region width at the surface of p-type Ge, and we demonstrate the manipulation of the hole carrier concentration p in the depletion region by using illumination with a blue light-emitting diode (LED) light source or laser, or a red laser (λ = 635 nm)

Summary

Introduction

The characterization of semiconductor materials and devices is key for understanding and developing semiconductor technologies. The changes and the controlled manipulation of charge carrier concentrations at semiconductor interfaces are of fundamental importance for their functionality in devices. With the tremendous growth of the field of semiconductor device physics and the advancement of experimental characterization techniques over the past decades, enormous progress has been achieved, providing insights and improvements of semiconductor devices [1,2,3]. A combination of macroscopic transport measurements and simple modeling are used to determine charge carrier depth profiles and electric field gradients across semiconductor interfaces [1,2].

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