Ga and In Autodoping of Cdt, MnxTe Epitaxial Layers Grown on GaAs and InSb Substrates
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Ga AND In AUTODOPING OF Cdt ,MnxTe EPITAXIAL LAYERS
GROWN ON GaAs AND kiSb SUBSTRATES J.J. DUBOWSKI*, J.M. WROBEL**, S. ROLFE*, J.A. JACKMAN+, J.H. MAZUR- AND J. NOADW Division of Physics, NRC, 100 Sussex Dr., Ottawa, Ont., Canada K1A 0R6 Department of Physics, University of Missouri, Kansas City, MO 641110, USA + Metals Technology Laboratories, CANMET, Ottawa, Ont., Canada KIA 031 ++ Materials Science Department, University of Southern California, Los Angeles, USA "#Communication Research Centre, Ottawa, Ont., Canada K2H 8S2 ABSTRACT A study of Ga and In outdiffusion into CdlXMnxTe ( 0 :s x s .70 ) epitaxial layers grown on (111)GaAs and (001)lnSb was carried out. The layers were grown by pulsed laser evaporation and epitaxy on substrates held at temperatures below 310 OC.The structural quality of the layers was examined using x-ray diffraction and transmission electron microscopy. Atendency toward precipitation of Ga at the near surface region of (11 1)CdMnTe grown on (11 1)GaAs, usually less than 300 nm wide, has been observed with secondary ion mass spectroscopy. Similar results were observed for the migration behaviour of In in (001)CdTe grown on (001)lnSb. The ion imaging revealed that both In and Ga accumulate near the surface at localized spots, up to about 10 pm in diameter. The concentration of the spots is in the range of 104 - 106 cmz. The Ga- and In-rich channels sometimes extend over the whole sample. Annealing at temperatures as low as 400 °C for 2 h significantly increases the concentration of the Ga spots and the average concentration of Ga in the films to above 1016 cm-3. Low-temperature photoluminescence data obtained for annealed samples do not indicate any structural deterioration typical for heavily doped Bridgman grown samples. A sharp neutral-donor bound-exciton transition (DO,X) is observed for samples with 0 < x < .10. INTRODUCTKON A continuing interest has been observed in the application of GaAs and InSb substrates for epitaxial growth of CdTe, HgCdTe and CdMnTe. Relatively mature technologies of CdTe, and HgCdTe on GaAs and InSb promise potential applications of these structures in IR detection1, 2 and high-speed MIS devices 3 . Epitaxial layers of CdMnTe are of particular interest due to their potential application in devices based on magneto-optical effects4 and as an alternative to CdTe substrate used in HgCdTe IR detectors. Performance of such devices will depend upon the ability to control the unintentional doping that takes place as CdTe or CdMnTe are grown on GaAs and InSb. Significant migration of Ga 5' 6 and In7,8 into epitaxial layers of CdTe grown on GaAs and InSb has been reported. Recently, we found9 that accumulation of Ga in localized spots takes place near the surface region of CdTe grown on GaAs. The presence of Ga was verified in such a case with low-temperature photoluminescence (PL)10 and electrolyte electroreflectance 11 measurements. In this paper, we describe the use of secondary ion mass spectroscopy (SIMS) and low-temperature PL to study Ga diffusion in (111)Cd
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