Spectroscopic determination of hole density in the ferromagnetic semiconductor Ga$_{1-x}$Mn$_{x}$As

TL;DR

This paper introduces a spectroscopic Raman scattering method to accurately measure hole density in GaMnAs semiconductors, overcoming limitations of traditional transport techniques affected by the anomalous Hall effect.

Contribution

It presents the first room-temperature Raman spectroscopy technique to determine hole density in GaMnAs, correlating it with Mn concentration and Curie temperature.

Findings

Hole density increases with Mn concentration up to 8.3%.

Unscreened LO phonon frequency decreases linearly with Mn doping.

Hole density correlates directly with Curie temperature.

Abstract

The measurement of the hole density in the ferromagnetic semiconductor Ga$_{1-x}$Mn$_{x}$As is notoriously difficult using standard transport techniques due to the dominance of the anomalous Hall effect. Here, we report the first spectroscopic measurement of the hole density in four Ga$_{1-x}$Mn$_{x}$As samples ($x=0, 0.038, 0.061, 0.083$) at room temperature using Raman scattering intensity analysis of the coupled plasmon-LO-phonon mode and the unscreened LO phonon. The unscreened LO phonon frequency linearly decreases as the Mn concentration increases up to 8.3%. The hole density determined from the Raman scattering shows a monotonic increase with increasing $x$ for $x\leq0.083$, exhibiting a direct correlation to the observed $T_c$. The optical technique reported here provides an unambiguous means of determining the hole density in this important new class of ``spintronic'' semiconductor materials.