E. Sörman

Electron effective masses and mobilities in high‐purity 6H–SiC chemical vapor deposition layers

The first observation of cyclotron resonance in 6H‐SiC by optically detected cyclotron resonance (ODCR) spectroscopy at X‐band microwave frequency is reported. High purity undoped, n‐type 6H‐SiC layers grown by chemical vapor deposition (CVD), with residual doping concentrations in the 1014–1015 cm−3 range, were investigated. Effective mass values were determined as m*⊥=(0.42±0.02)m0 and m*∥=(2.0±0.2)m0. From the fit of the ODCR line shape, a remarkably high mobility at 6 K was deduced: μ⊥≊1.1×105 cm2/V s for electrons in the basal plane. The anisotropy of the effective mass and the carrier mobility is discussed in comparison with previously reported data.

ORIGIN OF N-TYPE CONDUCTIVITY OF LOW-TEMPERATURE GROWN INP

It is shown with correlated magnetic resonance and electrical measurements that the PIn antisite is the prevailing defect in InP grown by molecular‐beam epitaxy at low temperature. The first ionization level of the PIn antisite is resonant with the conduction band, which makes the material n‐type conducting due to autoionization of the PIn antisite.

Possible lifetime‐limiting defect in 6H SiC

We reveal and investigate a possible lifetime‐limiting defect in as‐grown 6H SiC by optical detection of magnetic resonance (ODMR). This defect is shown to be a deep level center (with an energy level at about Ec−1.1 eV), evident from the related deep photoluminescence emission and a photo‐excitation spectrum of the ODMR signal. The fact that this defect has been observed in both bulk crystals and epilayers, regardless of their doping type, indicates that this must be a common and basic defect in 6H SiC.

Dominant recombination center in electron‐irradiated 3C SiC

Deep level defects and their role in carrier recombination processes in electron‐irradiated 3C SiC have been studied by photoluminescence (PL) and optically detected magnetic resonance (ODMR). An isotropic ODMR spectrum, with a g value of 2.0061±0.0002 and an effective electron spin S=1/2, is observed in irradiated 3C SiC films. From the spectral dependence studies of the ODMR signal, the defect is shown to be a deep level center related to a radiation‐induced PL band with a zero‐phonon line at 1.121 eV. Due to the competition between different carrier recombination channels, this ODMR spectrum can also be observed as a decrease of any other PL emissions from the sample, indicating its dominant role in recombination processes.

Optically detected magnetic resonance studies of low-temperature InP

We present experimental results from studies of low-temperature molecular beam epitaxially grown InP (LT InP), by optical detection of magnetic resonance (ODMR), where both the identification of defects and recombination processes can be studied simultaneously. The presence of the PIn antisites is unambiguously established, evident from the doublet hyperfine structure from the31P atom (with nuclear spin I=1/2 and 100% natural abundance). The PIn antisites are shown to be involved in strong nonradiative recombination processes, which compete with radiative ones via other defects. In addition to the PIn antisites, another defect has been detected in ODMR experiments which is shown to be a low-symmetry defect, likely a complex related to Be. Photo-excitation of the ODMR signals allows determination of the energy level positions of these defects. The results indicate that the PIn antisite is the prevailing defect governing the electronic properties of the material.

SiC – a semiconductor for high-power, high-temperature and high-frequency devices

SiC has in comparison with Si superior basic properties for applications in high-power, high-frequency and high-temperature electronics. The potential applications of SiC were known decades ago, but the poor quality of the material produced at that time has delayed the device development. However, during the last years the crystal growth process of SiC has been improved considerably. We will present some important properties of SiC, describe the two most common growth processes and discuss fundamental materials problems that remain to be solved. A further aspect, which we will discuss, is the polytypism of SiC, which may allow us to obtain generic knowledge of, for instance, defects in semiconductors.

Deep luminescent centres in electron-irradiated 6H SiC

Abstract We report on our observation of several new photoluminescence (PL) spectra in electron-irradiated 6H SiC. In addition to the vacancy-related PL spectrum ranging from 1.36 to 1.44 eV, four other spectra with no-phonon lines in the regions of 0.9983–1.0738 eV, 1.0878–1.1342 eV and 1.3563–1.3711 eV were detected in 6H SiC. These luminescent centres are rather thermally stable. From the formation and annealing behaviour, these centres were suggested to be complexes, of which some involve a silicon vacancy.

Effects of microwave fields on recombination processes in 4H and 6H SiC

The effects of microwave fields on recombination processes, which are responsible for the optical detection of cyclotron resonance (ODCR) in 4H and 6H SiC epitaxial layers, have been investigated. We present experimental evidence indicating that the dominant mechanism of ODCR in SiC, at low temperatures and in a common range of microwave power (<200 mW), is microwave-induced lattice heating under the cyclotron resonance conditions. The results also show that at low temperatures and low microwave power the dominant scattering mechanism is impurity scattering, while carrier scattering by lattice phonons dominates under high microwave power conditions.

Effects of a hot two-dimensional electron gas on optical properties of modulation-doped GaAs/AlGaAs heterostructures

The effects of a hot two-dimensional electron gas (2 DEG) on optical properties of modulation-doped GaAs/AlGaAs heterostructures have been investigated by photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. A decrease of the PL intensity from shallow excitons and an enhancement of the interband recombination between the 2 DEG (confined in a notch potential near the heterointerface) and photo-excited holes are observed, when the cyclotron resonance (CR) condition for electrons is fulfilled. The mechanisms responsible for these observations are discussed in terms of a hot 2 DEG heated in the microwave (MW) field. The angular dependence of the ODCR peak proves the 2D character of the corresponding hot electrons. In this way the authors identify these PL emissions as arising from the same GaAs active layer.

Optically detected magnetic resonance studies of defects in 3C SiC epitaxial layers

Abstract Optically detected magnetic resonance (ODMR) was used to study defects in 3C SiC epitaxial layers grown at high temperatures (1550°C) by chemical vapour deposition on a free-standing 3C SiC film substrate. An isotropic, very broad and asymmetric ODMR line was observed under ultraviolet light excitation. This line is shown to be due to the overlapping of two different isotropic spectra, as revealed by magnetic field modulation measurements. Both spectra can be described by an effective electron spin S = 1 2 . The higher field line with a g-value of 2.006 may be related to a silicon vacancy. Using below bandgap excitation, the lower field spectrum (g = 2.012) was found to have a triplet structure which could be due to the hyperfine of 14N. This defect is related to a new photoluminescence band in the region of 1.1–1.58 eV.