Quantitative optical variants of deep level transient spectroscopy: application to high purity germanium

Abstract

Two optical variants of deep level transient spectroscopy (DLTS) have been quantified and applied to n-type high-purity germanium (shallow concentration 109–1010 cm−3). In both methods, optical injection (using light of above band gap energy) at the back ohmic contact together with a suitable sample configuration (sandwich configuration) results in the detection of centers in the minority half of the bandgap. Different deep hole traps are clearly resolved and identified as mainly Cu related traps with concentrations in the 106–108 cm−3 range. In the first DLTS variant, known as optical DLTS or ODLTS, the spectrum is generated by capacitance transients whereas in the second, it is generated by current transients. The latter method, also known as photo induced (current) transient spectroscopy or PI(C)TS is especially suited for high resistivity or semi-insulating materials which can not be measured with capacitance based DLTS. The formulas to calculate the deep level concentrations from the DLTS spectra are derived and verified experimentally, making these two DLTS variants not only qualitative but also quantitative tools for deep level analysis (comparable to ‘classical’ capacitance DLTS).