No abstract

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.

Undoped n‐InP and Zn‐doped p‐InP are grown by the SSD method. Hall measurements on wafers cut from the polycrystalline n‐InP ingots give values between 1015 and 1016 cm−3 for the carrier concentration averaged over the crystallites of the wafer. From the electron mobilities measured at 77 K on single crystalline samples (maximally 5.0 × 104 cm2/Vs) it can be concluded on the high purity and perfection of this material. Zn doping yields p‐InP with p = (3 to 4) × 1016 cm−3and μ = (113 to 140) cm2/Vs atroom temperature. The hole mobilities at 77 K(1700 to 2160 cm2/Vs) are the highest ones reported for InP up to now. By fitting of the p(T) curves between 30 and 500 K concentrations and activation energies for the shallow acceptor Zn and for a medium deep acceptor present beside Zn are determined.

In undoped bulk-grown GaAs single crystals, which show a wide variation of the resistivity, a characteristic dependence of the Hall mobility on the carrier concentration with a pronounced minimum at about 1×1010 cm−3 is observed. By applying a standard effective medium theory it is shown that this minimum is caused by mesoscopic nonuniformities of the charge carrier concentration and not by increased scattering rates or additional scattering mechanisms as would be the standard interpretation in the case of homogeneous samples. These nonuniformities observed by high-resolution point-contact measurements are connected with the cellular structure of dislocations.