Mn Related Defect Levels in Germanium
2. Experimental conditions. The source material are single crystal germanium wafers, supplied by Umicore, with a shallow dopant concentration of 1014 cm-3 Ga and Sb for p- and n-type, respectively. To introduce Mn impurities, 99.995% pure Mn was thermally evaporated on the Ge surface. Afterwards the specimens were placed in a resistive furnace under Ar atmosphere for 10 minutes at 700°C. Finally, the residual Mn on the surface was removed by etching with a mixture of HNO3 and HF (3:1?). Schottky diodes for DLTS were prepared by evaporation of Au (n-type) or In (p-type) barriers immediately after etching. To identify the contamination introduced during the processing, Schottky diodes were also prepared on parts of the specimens outside the Mn covered areas. Schottky diodes on n-Ge were also prepared by annealing the n-Ge:Mn samples (after indiffusion at 700°C) to 400°C for 20 min in order to form a MnGe metallic alloy contact.
3. Results and discussion. Fig. 1 a shows the DLTS spectrum of n-Ge:Mn with a MnGe Schottky contact. A similar spectrum was recorded on the specimen with an Au-Schottky barrier. Conventional DLTS shows one electron trap (Mn-E1), while injection of minority carriers (Vp>0) reveals two additional levels (Mn-H1 and Mn-H2). Fig. 1 b shows the DLTS spectrum of p-type Ge, with presence of Mn-H1 and Mn-H2 only after Mn diffusion.
Figure 1: DLTS spectrum of a) n-Ge/MnGe diode. b) p-type Ge with and without Mn-difussion.
The electron trap Mn-E1 (E=0.36eV) and the hole trap Mn-H1 (E=0.14eV) correspond with the two levels reported before [1,2]. The Mn-H2 peak (E=0.34eV) has to our knowledge not been reported before in the context of transition metal impurities. Nonetheless, its appearance only in Mn diffused samples, its almost equal amplitude and concentration profile to Mn-H1 suggests that it is also related to substitutional Mn in Ge. This may indicate that the substitutional Mn defect can adopt 4 charge states in Ge, one of which certainly corresponds with 2-, as identified with EPR.
4. Conclusions. Three Mn related defect levels have been identified with DLTS. The striking similarity with previously published results for two of the observed levels suggest the assignment to substitutional Mn in germanium. The third level was not reported before but can most probably also be assigned to Mn.
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