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It is proved by Hall effect measurements on Te-doped GaP and on ZnSiP, that the thermal activation energies of the majority impurities depend on the minority impurity concentrations. A new theoretical explanation for this concentration dependence is presented.Mittels Halleffektmessungen an Te-dotiertem GaP und an ZnSiP, wird gezeigt, daB die thermischen Aktivierungsenergien der Majoritiitsstorstellen von der Konzentration der Minoritiitsstorstellen abhangen. Fur diese Konzentrationsabhiingigkeit wird cine neue theoretische E r k k u n g gegeben.It is well known that in doped and compensated semiconductors three types of conductivity mechanisms with different activation energies c3 < E~ < c1 can be found, in general (see e.g . [l]).To be specific we shall concentrate on a n n-type semiconductor in the following. I n this case c3 corresponds to the phonon-assisted hopping motion of electrons from neutral donors t o empty positive donors, the energy spread of the donor levels being caused by the fluctuating electric field of the charged impurities. This hopping motion is well understood on the basis of the theory of Miller and Abrahams The activation energy c1 is connected with the energy ED, necessary to excite an electron from a donor into the conduction band, and deviates from ED slightly due to the fact, that the temperature dependence of the mobility deviates from p -T P 3 l 2[5]. The energy E, or E D is of principle interest in semiconductor physics and technology. However, it is understood much less both theoretically and experimentally than cZ and E~: not only its absolute value for different impurities cannot be calculated theoretically in satisfying agreement with experimental results, but also its large concentration dependence (if measured as a thermal activation energy e.g. by Hall experiments) is not well established even experimentally as explained below.I n this paper we want to contribute both experimental results and a new theoretical explanation for the concentration dependence of E D of shallow impurities.The phenomenon of the concentration dependence of the thermal activation energy of impurity electrons into the nearest host energy band is known for more than

Larger hole concentrations and lower mobilities are measured by Raman scattering of p-GaP in comparison with results of Hall and conductivity investigations. The Hall factor which is responsible for the differences can be obtained bv these measurements and is discussed on the basis of a two-band model.

From polycrystalline GaP grown by the SSD method or by the pressure synthesis samples are prepared which contain single large‐angle grain boundaries. I‐U and C–U characteristics are measured across the grain boundaries and compared with EBIC investigations performed on the same specimen using the barriers of the grain boundary itself for charge collection. Electrical measurements refer to symmetric and asymmetric grain boundaries, whereas the EBIC picture shows an asymmetry also for electrically symmetric grain boundaries due to a strong dependence of the EBIC contrast on differences of the barrier heights not detectable by these electrical measurements. A model is proposed which enables quantitatively to calculate the EBIC current across the grain boundary also with applied bias voltages. The investigated grain boundaries show often local inhomogeneities.

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