저온 분자선 에피택시법을 이용한 GaMnAs 자성반도체 성장 및 특성 연구

Abstract

The LT-MBE (low temperature molecular beam epitaxy) allows to dope GaAs with Mn over its solubility limit. A 75 nm thick GaMnAs layers are grown on a low temperature grown LT-GaAs buffer layer at a substrate temperature of 260 °C by varying Mn contents ranged from 0.03 to 0.05. The typical growth rate for GaMnAs layer is fixed at 0.97 ㎛/h and the V/III ratio is varied from 25 to 34. The electrical and magnetic properties are investigated by Hall effect and superconducting quantum interference device(SQUID) measurements, respectively. Double crystal X-ray diffraction(DCXRD) is also performed to investigate the crystallinity of GaMnAs layers. The Tc of the Ga1-xMnxAs films grown by LT-MBE are enhanced from 38 K to 65 K as x increases from 0.03 into 0.05 whereas the TC becomes lower to 45 K when the V/III ratio increases up to 34 at the same composition of x=0.05. This means that the ferromagnetic exchange coupling between Mn-ion and a hole is affected by the growth condition of the enhanced V/III ratio in which the excess-As and As-antisite defects may be easily incorporated into GaMnAs layer.