Excitationhyphen;dependent emission in Mghyphen;, Behyphen;, Cdhyphen;, and Znhyphen;implanted GaAs

摘要

The lowhyphen;temperature properties of the excitationhyphen;dependent (moving) emissions in Mghyphen;, Behyphen;, Cdhyphen;, and Znhyphen;implanted GaAs layers are investigated with respect to changes in temperature and excitation intensity. The substrates used were epitaxial layers, melthyphen;grownnhyphen;type crystals, and Crhyphen;doped semihyphen;insulating crystals. Donor concentrations of thenhyphen;type substrates were in the range 5times;1013to 2times;1018electrons cmminus;3. Models explaining a large energy shift are presented for both Crhyphen;doped andnhyphen;type substrates. The moving emissions are classified into three different cases: (a) donorhyphen;acceptorhyphen;pair emission in relatively pure weakly compensated crystals; (b) donorhyphen;acceptorhyphen;pair emission in impure strongly compensated crystals; and (c) a radiation transition from the conductionhyphen;band tails to the valence band. The donorhyphen;acceptorhyphen;pair emission in the impure compensated crystals shows the shift to lower energy with an increase of temperature in the temperature range 4ndash;50thinsp;deg;K, while the donorhyphen;acceptorhyphen;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 nearhyphen;surface region due to the outhyphen;diffusion of the implanted atoms in Crhyphen;doped substrates, and the highly resistive layer between thephyphen; andnhyphen;type region innhyphen;type substrates. Additional compensating donors are found to be defecthyphen;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.