Excitation-dependent emission in Mg-, Be-, Cd-, and Zn-implanted GaAs

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Abstract
The low‐temperature properties of the excitation‐dependent (moving) emissions in Mg‐, Be‐, Cd‐, and Zn‐implanted GaAs layers are investigated with respect to changes in temperature and excitation intensity. The substrates used were epitaxial layers, melt‐grown n‐type crystals, and Cr‐doped semi‐insulating crystals. Donor concentrations of the n‐type substrates were in the range 5×1013 to 2×1018 electrons cm−3. Models explaining a large energy shift are presented for both Cr‐doped and n‐type substrates. The moving emissions are classified into three different cases: (a) donor‐acceptor‐pair emission in relatively pure weakly compensated crystals; (b) donor‐acceptor‐pair emission in impure strongly compensated crystals; and (c) a radiation transition from the conduction‐band tails to the valence band. The donor‐acceptor‐pair emission in the impure compensated crystals shows the shift to lower energy with an increase of temperature in the temperature range 4–50 °K, while the donor‐acceptor‐pair emission in pure crystals behaves in the usual manner. This is due to the increase in the random impurity potential. The large shift of emission peaks originates in the impure compensated regions, i.e., the near‐surface region due to the out‐diffusion of the implanted atoms in Cr‐doped substrates, and the highly resistive layer between the p‐ and n‐type region in n‐type substrates. Additional compensating donors are found to be defect‐type donors, As vacancies. The formation of As vacancies differs depending on the substrate materials. The role of the As vacancy in forming a compensated region is discussed.