The coexistence of two types of carriers (free electrons and free holes) in InN:Mg and their competition is demonstrated by the temperature and magnetic-field-induced change of the sign of thermopower (a) as well as the maximum entropy mobility spectrum analysis. The results confirm the existence of alternative carrier channels in addition to the n-type surface inversion layer and p-type bulk. They also show that In-polarity can be propitious for occurrence of p-type conductivity.

Electrical properties of non-intentionally doped (nid) InAs/GaSb Superlattice (SL) structures and p-nid-n detectors grown by Molecular Beam Epitaxy on GaSb substrate are reported. The SL structures were made of 600 periods of 8 InAs monolayers (MLs) and 8 GaSb MLs, for a total thickness of 3 mu m. This structure exhibited a cutoff wavelength in the midwave infrared (MWIR) domain, near 4.7 mu m at 80K. Electrical transport measurements, based on resistivity and Hall Effect measurements, were performed on SL structure after removing the conducting GaSb substrate with an appropriate technological process. Carrier concentrations and mobilities carried out as a function of temperature (77-300K) for magnetic fields in the 0-1 Tesla range are analyzed. A change in type of conductivity is observed. The nid SL layers is p-type at liquid Nitrogen temperature while is n-type at room temperature. These results are completed with diode characterizations based on current-voltage (I-V) and capacitance-voltage (C-V) measurements performed on p-nid-n devices with identical InAs/GaSb SL active zone.

In this communication we report on electrical properties of nonintentionally doped (nid) type II InAs/GaSb superlattice grown by molecular beam epitaxy. We present a simple technological process which, thanks to the suppression of substrate, allows direct Hall measurement on superlattice structures grown on conductive GaSb substrate. Two samples were used to characterize the transport: one grown on a semi-insulating GaAs substrate and another grown on n-GaSb substrate where a etch stop layer was inserted to remove the conductive substrate. Mobilities and carrier concentrations have been measured as a function of temperature (77-300 K), and compared with capacitance-voltage characteristic at 80 K of a photodiode comprising a similar nid superlattice.

We present a detailed investigation of the different factors that rule the temperature dependence of the AlGaN/AlN/GaN Hall-FET devices in the temperature range 300-500 degrees C. To understand the origin of the apparent increase in drive-in current density which affects devices above 300 degrees C, several series of experiments have been done. We checked: (i) the constitutive materials resistance to elevated temperature, (ii) the insulation of the buffer layer, (iii) the stability of the carrier density in the two-dimensional electron gas and, finally, (iv) the performance of devices after temperature cycling. We found that, both, the material properties and insulation of the buffer layers remains satisfactory up to 500 degrees C. The carrier density remains also very stable. However, we observe some material deterioration after temperature cycling which suggests that, in such non-passivated devices, the thermal drift could be due to partial deterioration of the surface layers and/or the gate Schottky contact. (C) 2008 Elsevier B.V. All rights reserved.

In this communication, we report on electrical transport measurements of non-intentionally doped InAs/GaSb Super lattice structures grown by Molecular Beam Epitaxy. Resistivity and Hall Effect measurements were performed on two samples, corresponding to the same SL structure that has been grown on two different substrates: one on semi-insulating GaAs substrate, another on n-type GaSb substrate. To carry out the electrical measurements, the conducting GaSb substrate of the second sample has been removed. The study were performed in the temperature range 77-300K, for magnetic fields of 0.38 T.. The both samples exhibited a change in type of conductivity from p-type at low temperature to n-type near room temperature.

In this paper we present the resistivity and Hall-effect measurements on p-type GaN doped with Mg. The experiments were carried out as a function of hydrostatic pressure Lip to 1200 MPa in the temperature range 260-400 K. Both bulk GaN crystals as well as GaN: Mg epilayers were studied. In the investigated samples the decrease of resistivity and increase of hole concentration under pressure was observed. Such a behavior, which is contrary to the n-type material strongly suggests a decrease of the ionization energy of Mg acceptor (E-a = 183 meV) with pressure. This shift is very weak, less than -2 meV/GPa. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this paper, we present resistivity and Hall measurements on InAs/GaSb Superlattice (SL) grown by Molecular Beam Epitaxy (MBE) on GaAs semi-insulating substrate. Measurements have been carried out under hydrostatic pressure up to 1300 MPa in the temperature range 80-300 K. We observe that the sample exhibits a reproducible change in conductivity type. The SL is n-type at high temperatures range whereas it is p-type at low temperature. The characteristic temperature T-ch at which the switch of conductivity type occurs increases with pressure from T-ch = 190 K to 280 K at highest pressure. The room temperature results are characterized by a strong increase of resistivity with pressure. The room-temperature Hall mobility varies from 1350 cm(2)/V s for ambient pressure to 345 cm(2)/V s for P = 1210 MPa. This strong effect of pressure on electrical transport properties of material suggests that at room temperature at least two types of electrons respectively with high and low mobility take part in the conduction process. The low mobility carriers could be related to the L mini band. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim