DI ST RI BU TI ON Controlling the growth morphology and phase segregation of Mn - doped Ga 2 Se 3 on Si ( 001 )

The growth and phase segregation properties of the potential dilute magnetic semiconductor alloy, (MnSe)x(Ga2/3Se)1−x, are studied as a function of thickness, Mn concentration, post-growth annealing, and the presence or absence of undoped Ga2Se3 buffer and capping layers. This system is an unusual case in heteroepitaxy where two phase MnSe+Ga2Se3 has better lattice matching than the (MnSe)x(Ga2/3Se)1−x alloy. Despite this peculiarity, this system shows a modified form of Stranski-Krastonow growth: laminar films are observed up to a certain x-dependent critical thickness, above which islands are observed by scanning tunneling microscopy (STM). The island morphology depends on the presence or absence of an undoped Ga2Se3 buffer layer and postgrowth annealing. A kinetically stabilized platelet morphology is observed at the crossover point between laminar and islanded films. Based on Mnand SeK edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES), there are two types of Mn in islanded films: Mn that remains doped in the Ga2Se3 but oxidizes upon exposure to air, and Mn that participates in the islands, which are precipitates of the MnSe phase. Consistent with MnO or MnSe, L-edge X-ray absorption on air exposed films suggests the Mn is in the formal 2+ oxidation state. No L-edge X-ray magnetic circular dichroism (XMCD) signal is observed at 20 K, which may be due to surface effects or to a lack of magnetic order.