DLTS Measurements of Trapping Defects in High Purity Germanium

The greatly enhanced solubility of Cu in Ge containing excess vacancies has been demonstrated, and cleaning procedures which prevent Cu contamination during annealing are described. The energy level of the "80 meV" vacancy-hydrogen complex is found by Hall effect measurements to be 71 ± 1 meV, assuming a degeneracy of 4. Another level of undetermined origin was also observed at Ev + ~35 meV. When Cu is introduced, the Hall effect curves show the presence of the well-known 40 meV level of singly ionized substitutional Cu and another level near 62 meV, again assuming g=4. Eleven defect levels have been detected by DLTS and have been assigned numbers corresponding to the temperatues where they appear using a rate window of ¿max = 0.116 ms. Peak 48 is the vacancy-hydrogen complex seen in dislocation-free Ge. Peaks associated with Cu are found at 27, 43, 119, and 167. Another defect which does not involve Cu also shows up prominently at 27. This peak and another at 56 are most frequently observed in material that shows trapping and high concentrations of "smooth pits". A peak at 19 is caused by dislocations. Lesser peaks at 84, 100, 137, and 195 have also been observed. The energy levels, and emission and capture probabilities of the more prominent defects have been measured, enabling their effectiveness as trapping centers to be calculated.