Analysis of Cr-Doped CdGeAs 2 Using Thermal Admittance Spectroscopy
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University of Dayton Physics Department, 300 College Park, Dayton, OH 45469-2314
SSanders, A Lockheed Martin Company, Nashua NH 03061-2035
ABSTRACT The optical and electrical properties of chrome-doped CdGeAs2 (CGA), an important non-linear optical material, are reported. CGA, a chalcopyrite semiconductor of the pseudoIII-V type, is a close ternary analog to GaAs, possessing significant differences. To date, the electrical and optical properties of as-grown undoped CGA have been controlled by a somewhat shallow dominant residual acceptor which it is the source of significant undesirable optical absorption. Highly transparent semi-insulating CGA should be attainable using compensation and counterdoping schemes similar to those used for GaAs. However, identifying suitable deep and shallow n-type and p-type dopants will require extensive empirical studies. As a starting point of survey to find deep levels, the properties of CGA:Cr have been investigated. Cr is a reasonable choice as it has been used extensively to provide a deep level in GaAs. Thermal Admittance Spectroscopy was used to examine the electrically active levels in this material. These measurements were correlated with temperature dependent Hall effect measurements, and IR absorption measurements. SIMS analysis was utilized to estimate the Cr concentration as the segregation coefficient for Cr in CGA has not been reported.. The results show that there is a p-type level introduced into the band gap at about 0.16 eV above the valence band, a value nominally 50% deeper than that of the native acceptor. The background doping as measured by Capacitance-Voltage measurements was determined to be 8 x 1016 cm 3 near the surface, and 1.0 X 1017 cm3 in the bulk. These results are compared to similar measurements in undoped material.
INTRODUCTION CdGeAs2 is a member of the family of ternary chalcopyrite compounds that have attracted interest in recent times for their nonlinear optical properties. They have potential for applications as optical parametric oscillators and frequency converters for the infrared, and a range of other optoelectonic devices. CdGeAs 2 has one of the highest non-linear optical coefficients (d36 = 236 pm/V), and the transmission band is wide, ranging from 2.3 gim to 18 gim. It also possesses a relatively high thermal conductivity and a strong birefringence.' Recent progress in the growth technology has resulted in large, crack-free, single crystals. These crystals are suitable for use in OPO and frequency doubling devices. One of the obstacles to the realization of this potential is undesired optical absorption in the transparency range near the fundamental band edge induced by lattice-related defects. 2 465 Mat. Res. Soc. Symp. Proc. Vol. 607 ©2000 Materials Research Society
Improvements Improvemen in transparency have been achieved by several methods. Electron irradiation has been
Singly &Doubly Doped
Compensation Schemes CdGeAs 2RT Energy gep : 0.67 s
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