A study was made of the effect of an As over-pressure upon Mn diffusion. The sources of Mn included solid Mn thin films, which were deposited directly onto the GaAs substrate, and Mn vapor from pure solid Mn, MnAs, or Mn3As. When a solid Mn film was used as the diffusion source, a non-uniform dopant distribution and a poor surface morphology was obtained. This was due to reaction between the Mn film and the GaAs matrix. The degraded surface consisted of a layer of polycrystalline cubic alloy with a lattice constant of almost 0.84nm, and with a composition that was close to Ga2Mn; with a small amount of As. Of the remaining diffusion sources, only MnAs consistently produced a uniform doping distribution and a smooth surface morphology. By diffusion at 800C, a uniform surface hole carrier concentration as high as 1020/cm3 could be obtained by using MnAs as a source. The As over-pressure was found to alter drastically the Mn diffusion profile and Mn, like Zn, could diffuse interstitial-substitutionally. Vapor from Mn or Mn3As degraded the surface. However, Mn3As degraded the surface more rapidly. A sufficiently high As over-pressure completely suppressed surface degradation.

C.H.Wu, K.C.Hsieh: Journal of Applied Physics, 1992, 72[12], 5642-8