The electrical conductivity and the Hall effect are investigated in the temperature region fiom 77 to loo0 K on undoped ZnO single crystals grown by vapour phase transport. The growth conditions were systematically altered to get crystals with definite non-stoichiometry. The electrical properties are related to these growth conditions. The analysis of the Hall data yields the phase boundary ZnO/Zn and a formation enthalpy of 1.5eV for the dominant native donor. This donor is suggested to be the oxygen vacancy. The Hall mobility is analysed with regard of new aspects giving a smaller anisotropy than in earlier analyses. An undotierten durch Gasphasentransport geziichteten ZnO-Einkristallen werden elektrische Leitfiihigkeit und Halleffekt im Bereich von 77 bis 1000 K untersucht. Durch Anderung der Ziichtungsbedingungen konnen definierte Grade der Nichtstoichiometrie erzeugt werden, was in den elektrischen Eigenschaften deutlich zum Ausdruck kommt. Die Analyse der Hallmessungen ergab die Phasengrenze ZnO/Zn sowie eine Bildungsenthalpie von 1,5 eV fur den dominierenden Eigendonator, der als Sauerstoffvakanz interpretiert wird. Die Analyse der Hallbeweglichkeit ergibt eine geringere Anisotropie als in friiheren Arbeiten.

O B H a p y m e I -I a q p e 3~b 1~a f i~o M a J I a a nonyruupmra JIHHHM, paman 0,3 cm-l. r I p~ 77 K

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

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.

Hall effect and conductivity in undoped low-resistivity n-type ZnSiP, single crystals as grown from melt and by vaponr phase transport were measured in the temperature range from 77 up to 900 K. Hall mobilities in various samples ranged from 15 to 240 cm2/Vs a t room temperature. Analysis of the Hall data of crystals from melt by means of a least square f i t yields a density of states effective mass of (0.11 0.02) m,,. The concentration dependence of the donor activation energy may be approximated by a linear relationship between E D and the cubic root of the donor concentration N D . I m Temperaturbereich 77 bis 900 K wurden an undotierten n-leitenden ZnSiP,-Einkristallen, die aus der Schmelze und mittels Gasphasentransport hergestellt wurden, Halleffekt und Leitfahigkeit gemessen. Die Hallbeweglichkeiten lagen fur die verschiedenen Proben im Bereich von 15 bis 240 cm2/Vs. Die Analyse der Halleffekt-Kurven der aus der Schinelze geziichteten Kristalle mittels nichtlinearer Ausgleichsrechnung lieferte eine effektive Zustandsdichtemasse von ( 0 , l l f 0,02) m,. Die Abhangigkeit der Donatoraktivierungsenergie von der Donatorkonzentration kann durch eine lineare Reziehung zwischen E D und der dritten Wurzel aus N D angenahert werden. 41 *