We have performed nitrogen and phosphorus co-implants at room temperature to obtain high n-type carrier concentration layers in SiC. An inductive heating RTA furnace has been used for the activation annealing. The influence of the temperature ramp parameters such as rise/decrease temperature speed and intermediate annealing steps on the dopant activation rate and surface morphology have been investigated. A reduction of the temperature ramp slope reduces the surface roughness by 50%. Inclusion of a pre-activation annealing step at low temperatures (1300 degrees C) further reduces the surface roughness. However, the use of slower ramps or an intermediate annealing step during ramp up reduces the free carrier concentration. The faster the ramp up, the higher the activation rate and the resulting doping. We also demonstrate that the inclusion of a post-activation annealing at intermediate temperatures (1150 degrees C) reduces significantly the surface roughness. In addition, the use of this post-annealing treatment does not degrade the activation rate nor the carrier Hall mobility, and activation rates close to 100% have been obtained.

We report on investigation of p-type doped, SiC wafers grown by the Modified-Physical Vapor Transport (M-PVT) method. SIMS measurements give Al concentrations in the range 10(18) to 10(20) cm(-3), with weak Ti concentration but large N compensation. To measure the wafers' resistivity, carrier concentration and mobility, temperature-dependant Hall effect measurements have been made in the range 100-850 K using the Van der Pauw method. The temperature dependence of the mobility suggests higher Al concentration, and higher compensation, than estimated from SIMS. Additional LTPL measurements show no evidence of additional impurities in the range of investigation, but suggest that the additional compensation may come from an increased concentration of non-radiative centers.

The electrical resistivity of 4H-SiC doped with nitrogen is analyzed in the temperature range 10-700 K for nitrogen concentrations between 3.5x10(15) and 5x10(19) cm(-3). For the highest doped samples, a good agreement is found between the experimental resistivity and the values calculated from a generalized Drude approach at similar dopant concentration and temperature. From these results, the critical concentration (N-c) of nitrogen impurities which corresponds to the metal-nonmetal transition in 4H-SiC is deduced. We find N-c similar to 10(19) cm(-3).

We report a detailed investigation of the electrical properties of p-type 4H-SiC. In the range 100 K-800 K we show that, both, the temperature dependence of the hole concentration and Hall mobility is satisfactorily described using the relaxation time approximation. Performing a detailed comparison of in-situ vs. implantation doping, we evidence an incomplete activation of the dose (about 50 ± 10 %) with apparition of a large number of compensating centres in the implanted layers.

Electrical transport phenomena have been investigated in (Al,Ga)N/GaN heterostructures (without any intentional doping) with an Al content ranging from 10 to 32 %. Conductivity and Hall Effect measurements have been performed as a function of temperature up to 700 K. To analyse the temperature dependence of the two-dimensional electron gaz concentration (2DEG) n, a fully self-consistent calculation (coupled Schrodinger and Poisson equations), was developed for the conduction band edge of the heterostructures. The observed 2DEG concentration changes vs. temperature have been compared with the theoretical predictions taking into account the electric fields in the structure and the surface states. A calculation based on the relaxation time approximation has been developed to describe the temperature dependence of the mobility. The electrical performance of GaN/AlxGa1-xN heterostructures with x=0.32 % indicate that they could be good candidates for Hall sensor working at high temperature (up to 600 K). At room temperature, the magnetic field sensitivity is K K-H0= 60 V/A/T. Its temperature sensitivity S, is lower than +500 ppm/K up to 600K. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In order to process n-type channel MOSFETs on (11 (2) over bar0)-oriented 4H-SiC wafers one has to optimise, independently, many different steps. First is the growth of the active epitaxial layer, including the effect of p-type doping. Next is the oxidation and, finally, the n-type implantation for source and drain formation. In this work, we investigate the growth and doping of the p-type doped epitaxial layer on the (1120)-oriented substrate using, both, SIMS, low temperature photoluminescence measurements and Hall effect measurement to control the final doping level. Next we investigate the change in oxidation kinetics with respect to the conventional (0001) surfaces. Finally, we evaluate the efficiency of implantation and annealing processes. (c) 2005 WILEY-VCH Verlag GmbH I Co. KGaA, Weinheim.

We report an experimental investigation of the residual (n-type) and intentional (p-type) doping level of < 11-20> epitaxial layers grown on a-cut 4H-SiC substrates. Using SIMS, C(V) measurements, low temperature photoluminescence and Hall effect investigations, we show that nitrogen incorporates 3 times more than usually found for < 0001> surfaces. Conversely, aluminum incorporates 8 times less. Altogether, this is in excellent agreement with previous results from stepcontrolled epitaxy.