Leroy L. Chang

Morphology of MBE grown InAs films studied by atomic force microscope

Abstract The morphology of MBE grown InAs films on GaSb buffered GaAs(0 0 1) substrates with miscuts ranging between 0.2° and 4° has been studied by atomic force microscope (AFM). Step flow growth mode on nominal singular (1 0 0) substrates has been observed for samples grown at substrate temperatures higher than 500°C and for samples on miscut substrates grown at temperatures between 400°C and 530°C. Unstable growth mode has been observed on nominal singular (0 0 1) substrates when substrate temperatures are lower than 450°C. Relatively high density pits have also been observed on InAs surfaces with nucleation temperatures above 450°C.

Investigation of Local Structures Around Mn Atoms in In 1-x Mn x As Diluted Magnetic Semiconductors Using Exafs

Extended x-ray absorption fine structure (EXAFS) techniques have been used to investigate the local structures in In l-x Mn x As films grown by molecular beam epitaxy (MBE) under different processing conditions. For samples grown at low substrate temperatures (near 200°C) or with a low Mn concentration (about 1 atomic%), the Mn atoms can substitute for In in the InAs host, thus indicating that III-V diluted magnetic semiconductors (DMS) can indeed be prepared by substitutional doping of magnetic impurities. On the other hand, substitution dose not take place in high Mn concentration (above 10%) samples grown at high substrate temperatures (around 300°C); these samples contain a large amount of MnAs clusters and become ferromagnetic

Formation of Mn-As Centers in In 1-x Mn x As Diluted Magnetic Semiconductors

XAFS spectra at the Mn K-edge were obtained for films of In 1-x Mn x As (0.0014 ≤x ≤ 0.12) grown by MBE method at two different substrate temperatures T s , = 200–210 °C and T s , = 280–300 ° C. It has been found that Mn-As complexes which consist of a central Mn atom surrounded by six neighboring As most likely arranged in the form of a distorted trigonal antiprism with one or two additional Mn atoms placed on the long axis of the antiprism, can substitute for the In-As tetrahedron in the undistorted zincblende structure. For a composition of x = 0.12 we have found the formation of MnAs clusters with NiAs-like structure in the high-growth-temperature samples. We thus conclude that the magnetic properties of the In 1-x Mn x As semiconductors are mainly determined by the formation and local structure olthe Mn-As complexes.