The origin and the formation mechanism of a surface morphological defect in 4H-SiC epilayers are reported. The defect appears on the surface of an epilayer as an inclined line-like feature at an angle of +/- 80 degrees to the step-flow direction [ 11 2 over bar 0 ] . The defect is confirmed to originate from a threading screw dislocation intersecting the surface and its orientation is controlled by the sign of the Burgers vector of the dislocation. The defect forms through the interaction of local spiral growth associated with threading screw dislocations and step-flow growth related to the substrate offcut. The defect mainly appears in the epilayers grown through chloride-based chemistry, where in situ surface preparation of the substrate is performed in H-2 + HCl at a relatively high temperature.

Silicon Carbide (SiC) is a wide bandgap semiconductor that has attracted a lot of interest for electronic applications due to its high thermal conductivity, high saturation electron drift velocity and high critical electric field strength. In recent years commercial SiC devices have started to make their way into high and medium voltage applications.

Despite the advancements in SiC growth over the years, several issues remain. One of these issues is that the bulk grown SiC wafers are not suitable for electronic applications due to the high background doping and high density of basal plane dislocations (BPD). Due to these problems SiC for electronic devices must be grown by homoepitaxy. The epitaxial growth is performed in chemical vapor deposition (CVD) reactors. In this work, growth has been performed in a horizontal hot-wall CVD (HWCVD) reactor. In these reactors it is possible to produce high-quality SiC epitaxial layers within a wide range of doping, both n- and p-type.

SiC is a well-known example of polytypism, where the different polytypes exist as different stacking sequences of the Si-C bilayers. Polytypism makes polytype stability a problem during growth of SiC. To maintain polytype stability during homoepitaxy of the hexagonal polytypes the substrates are usually cut so that the angle between the surface normal and the c-axis is a few degrees, typically 4 or 8°. The off-cut creates a high density of micro-steps at the surface. These steps allow for the replication of the substrates polytype into the growing epitaxial layer, the growth will take place in a step-flow manner. However, there are some drawbacks with step-flow growth. One is that BPDs can replicate from the substrate into the epitaxial layer. Another problem is that 4H-SiC is often used as a substrate for growth of GaN epitaxial layers. The epitaxial growth of GaN has been developed on on-axis substrates (surface normal coincides with c-axis), so epitaxial 4H-SiC layers grown on off-axis substrates cannot be used as substrates for GaN epitaxial growth.

In efforts to solve the problems with off-axis homoepitaxy of 4H-SiC, on-axis homoepitaxy has been developed. In this work, further development of wafer-scale on-axis homoepitaxy has been made. This development has been made on a Si-face of 4H-SiC substrates. The advances include highly resistive epilayers grown on on-axis substrates. In this thesis the ability to control the surface morphology of epitaxial layers grown on on-axis homoepitaxy is demonstrated. This work also includes growth of isotopically enriched 4H-SiC on on-axis substrates, this has been done to increase the thermal conductivity of the grown epitaxial layers.

In (paper 1) on-axis homoepitaxy of 4H-SiC has been developed on 100 mm diameter substrates. This paper also contains comparisons between different precursors. In (paper 2) we have further developed on-axis homoepitaxy on 100 mm diameter wafers, by doping the epitaxial layers with vanadium. The vanadium doping of the epitaxial layers makes the layers highly resistive and thus suitable to use as a substrate for III-nitride growth. In (paper 3) we developed a method to control the surface morphology and reduce the as-grown surface roughness in samples grown on on-axis substrates. In (paper 4) we have increased the thermal conductivity of 4H-SiC epitaxial layers by growing the layers using isotopically enriched precursors. In (paper 5) we have investigated the role chlorine have in homoepitaxial growth of 4H-SiC. In (paper 6) we have investigated the charge carrier lifetime in as-grown samples and traced variations in lifetime to structural defects in the substrate. In (paper 7) we have investigated the formation mechanism of a morphological defect in homoepitaxial grown 4H-SiC.

We report on a very low density (<5×1011 cm-2) of near-interface traps (NITs) at the Al2O3/4H-SiC interface estimated from capacitance-voltage (CV) analysis of MOS capacitors at different temperatures. The aluminum oxide (Al2O3) is grown by repeated deposition and subsequent low temperature (200°C) oxidation for 5 min of thin (1-2 nm) Al layers using a hot plate. We refer to this simple method as hot plate Al2O3. It is observed that the density of NITs is significantly lower in the hot plate Al2O3 samples than in samples with Al2O3 grown by atomic layer deposition (ALD) at 300°C and in reference samples with thermally grown silicon dioxide grown in O2 or N2O ambient.

Over 150 μm thick epilayers of 4H-SiC with long carrier lifetime have been grown with a chlorinated growth process. The carrier lifetime have been determined by time resolved photoluminescence (TRPL), the lifetime varies a lot between different areas of the sample. This study investigates the origins of lifetime variations in different regions using deep level transient spectroscopy (DLTS), low temperature photoluminescence (LTPL) and a combination of KOH etching and optical microscopy. From optical microscope images it is shown that the area with the shortest carrier lifetime corresponds to an area with high density of structural defects.

We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4H-SiC and their 6H-SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n- and p-type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

The influence of chlorine has been investigated for high growth rates of 4H-SiC epilayers on 4o off-cut substrates. Samples were grown at a growth rate of approximately 50 and 100 μm/h and various Cl/Si ratios. The growth rate, net doping concentration and charge carrier lifetime have been studied as a function of Cl/Si ratio. This study shows some indications that a high Cl concentration in the growth cell leads to less availability of Si during the growth process.

4H-SiC epilayers grown by standard and chlorinated chemistry were analyzed for their minority carrier lifetime and deep level recombination centers using time-resolved photoluminescence (TRPL) and standard deep level transient spectroscopy (DLTS). Next to the well-known Z(1/2) deep level a second effective lifetime killer, RB1 (activation energy 1.05 eV, electron capture cross section 2 x 10(-16) cm(2), suggested hole capture cross section (5 +/- 2) x 10(-15) cm(2)), is detected in chloride chemistry grown epilayers. Junction-DLTS and bulk recombination simulations are used to confirm the lifetime killing properties of this level. The measured RB1 concentration appears to be a function of the iron-related Fe1 level concentration, which is unintentionally introduced via the corrosion of reactor steel parts by the chlorinated chemistry. Reactor design and the growth zone temperature profile are thought to enable the formation of RB1 in the presence of iron contamination under conditions otherwise optimal for growth of material with very low Z(1/2) concentrations. The RB1 defect is either an intrinsic defect similar to RD1/2 or EH5 or a complex involving iron. Control of these corrosion issues allows the growth of material at a high growth rate and with high minority carrier lifetime based on Z(1/2) as the only bulk recombination center.