Structural, electrical, and magneto-optical characterization of paramagnetic GaMnAs quantum wells

TL;DR

This study demonstrates improved optical quality and reduced defects in GaMnAs quantum wells grown at higher temperatures, enabling detailed magnetic and electronic characterization of these paramagnetic semiconductors.

Contribution

It reports the growth of high-quality GaMnAs quantum wells at elevated temperature, with detailed analysis of Mn incorporation, defect reduction, and spin dynamics.

Findings

High Mn substitutional incorporation (70-90%) at 400°C

Observation of polarization-resolved photoluminescence and spin dynamics

No evidence of long-range Mn spin coupling

Abstract

Growth of GaMnAs by molecular beam epitaxy is typically performed at low substrate temperatures (250C) and high As overpressures leading to the incorporation of excess As and Mn interstitials, which quench optical signals such as photoluminescence (PL). We report on optical-quality Ga(1-x)Mn(x)As/Al(0.4)Ga(0.6)As quantum wells (QWs) with x < 0.2% grown at a substrate temperature of 400C. Electrical and structural measurements demonstrate that this elevated temperature reduces As defects while allowing the substitutional incorporation of Mn into Ga sites. From a combination of Hall and secondary ion mass spectroscopy measurements we estimate that at least 70-90% of the Mn incorporates substitutionally in all samples studied. The incorporation behavior shows both a substrate temperature and QW width dependence. The lower defect density of these heterostructures, compared to typical lower temperature grown GaMnAs, enables the observation of both polarization-resolved PL and coherent electron spin dynamics, from which the conduction band exchange parameter is extracted. No evidence of long-range Mn spin coupling is observed, whereas negative effective Curie temperatures indicate spin heating due to photoexcitation. The electron spin lifetime is maximized for light Mn doping and shows little magnetic field dependence indicating that the Dyakonov-Perel mechanism is dominant in these structures. PL spectra reveal a low energy peak from shallow donors, which because of the paramagnetic behavior of its PL polarization, we ascribe to Mn interstitials.