Curie temperature and carrier concentration gradients in MBE grown GaMnAs layers

TL;DR

This study investigates the magnetic and electronic properties of GaMnAs layers grown by low-temperature MBE, revealing a surface-to-interface gradient in Curie temperature and carrier concentration, which impacts the material's ferromagnetic behavior.

Contribution

It demonstrates the presence of a Curie temperature gradient in GaMnAs layers and correlates it with carrier concentration variations, providing insights into growth-related inhomogeneities.

Findings

Curie temperature decreases from surface to interface.

Carrier concentration is higher at the surface than at the interface.

Homogeneous Mn distribution confirmed by x-ray diffraction.

Abstract

We report on detailed investigations of the electronic and magnetic properties of ferromagnetic GaMnAs layers, which have been fabricated by low-temperature molecular-beam epitaxy. Superconducting quantum interference device measurements reveal a decrease of the Curie temperature from the surface to the GaMnAs/GaAs interface. While high resolution x-ray diffraction clearly shows a homogeneous Mn distribution, a pronounced decrease of the carrier concentration from the surface towards the GaMnAs/GaAs interface has been found by Raman spectroscopy as well as electrochemical capacitance-voltage profiling. The gradient in Curie temperature seems to be a general feature of GaMnAs layers grown at low-temperature. Possible explanations are discussed.