The effects of uniaxial compression and of hydrostatic pressure on the direct and indirect tunneling processes in germanium tunnel diodes have been studied experimentally under forward and reverse bias at 4.2*K and compared with Kane's theory. The diodes were formed by alloying indium doped with 3/8 weight per cent gallium on (100) and (110) faces of germanium bars containing an antimony concentration of 5.5 x 10 1 8 /cm 3 . The first order change of the tunneling current with stress was

more »

... d at fixed bias voltages. For biases smaller than 8 mv the current is direct and not affected by the relative shifts of the (111) conduction band valleys. In the bias range of indirect tunneling the anisotropic tunneling from the (111) valleys was observed in agreement with theory. In the range of direct tunneling to the (000) conduction band, the current change is correlated with the stress induced change of the d4rect band gap and of the energy separation between the (111) and (000) conduction bands. This separation was found to be 0.160 ± 0.005 ev 4t zero stress in agreement with optical measurements on degenerate germanium. Some details of the bias dependence of the pressure effeqt including some fine structure at small biases remain unexplained. Electrical transport measurement have been made on p-type ZnTe and n-type ZnSe. In ZnTe crystals doping with Cu, Ag and Au produces acceptor levels at 0.15, 0.11, and 0.22 ev respectively. An acceptor with an ionization energy of 0.048 ev was found in the undoped crystals and is identified as the first charge state of the Zn-vacamey. A e 1low 4ia. donor state, at approximately 0.01 ev below the conduction band, was found in n-type ZnSe. It also proved possible to prepare degenerate ZnSe. The scattering mechanisms limiting the lattice mobilities of both materials were considered. It was found that the polar interaction with the longitudinal optical phonons dominates the scattering of electrons in ZnSe. This mechanism probably also predominates in the scattering of the holes in ZnTe. However, the non-polar interaction with the optical modes could also contribute significantly if the appropriate coupling parameter is larger than we presently believe. Luminescence from p-n junctions constructed from the mixed crystal GaAsl xP x and from GaSb has been studied. Visible red radiation is produced by the former, but at present the efficiency is poor and the junction profile is quite irregular, presumably because of poor crystal structure. Attempts to produce coherent radiation from these junctions has thus far been unsuccessful. -5- SEMICONDUCTOR DEVICE CONCEPTS A. The Effect of Elastic Strain on Interband Tunneling in Sb-Doped Germanium (H. Fritzsche and J. J. Tiemann) The research reported here evolved from experiments carried out under Contract AF 19(604)-6623 which preceded the present one. These early investigations were described in Reports 3A and 4A of that contract, dated 23 December 1960 and 28 March 1961. In view of this history it see appropriate to present here a report of this work which has now reached a satisfactory conclusion.