Off-oriented Substrates Research Articles

High-Volume SiC Epitaxial Layer Manufacturing-Maintaining High Materials Quality of Lab Results in Production

Typically, research and development (R&D) results of epitaxial layer growth show superior properties of the grown layers compared to high volume results. Layer uniformities are excellent and achieved defect densities are low compared to typical results. In particular, the conversion of basal plane dislocations (BPD) from the silicon carbide (SiC) substrate is in focus to reduce bipolar degradation of p-n-junctions. It is a great challenge to maintain those excellent results in high-volume manufacturing considering all the factors that impact the properties of the epilayer. Thus, quality of the layers, high throughput and low cost have to be assessed to find a compromise between these key factors. In this paper we present results on the growth of epitaxial layers on 150 mm and 200 mm 4° off-oriented 4H-SiC substrates using warm-wall multi-wafer chemical vapor deposition (CVD) systems. Single wafer data of the key epitaxial layer parameters, thickness, doping and defect densities, are compared to batch and lot results, as well as to statistical data of several hundreds of wafers produced. Improvements in wafer-to-wafer (w-t-w) doping uniformity could be achieved for instance by implementation of an on-wafer temperature measurement. Substrate impact on defect levels is shown comparing X-ray topography (XRT) results of bare substrate wafers and defect analysis of epilayers on sister wafers from the same crystal. Statistical defect data and resulting predicted yield loss also show a dependence on substrate suppliers. For the first time we show w-t-w and run-to-run (r-t-r) results of doping and thickness measurements on 200 mm substrates. Also, defect results of epilayers on 200 mm wafers are compared to results on 150 mm.

A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates

We present a comparative study of the C-face and Si-face of 3C-SiC(111) grown on off-oriented 4H-SiC substrates by the sublimation epitaxy. By the lateral enlargement method, we demonstrate that the high-quality bulk-like C-face 3C-SiC with thickness of ~1 mm can be grown over a large single domain without double positioning boundaries (DPBs), which are known to have a strongly negative impact on the electronic properties of the material. Moreover, the C-face sample exhibits a smoother surface with one unit cell height steps while the surface of the Si-face sample exhibits steps twice as high as on the C-face due to step-bunching. High-resolution XRD and low temperature photoluminescence measurements show that C-face 3C-SiC can reach the same high crystalline quality as the Si-face 3C-SiC. Furthermore, cross-section studies of the C- and Si-face 3C-SiC demonstrate that in both cases an initial homoepitaxial 4H-SiC layer followed by a polytype transition layer are formed prior to the formation and lateral expansion of 3C-SiC layer. However, the transition layer in the C-face sample is extending along the step-flow direction less than that on the Si-face sample, giving rise to a more fairly consistent crystalline quality 3C-SiC epilayer over the whole sample compared to the Si-face 3C-SiC where more defects appeared on the surface at the edge. This facilitates the lateral enlargement of 3C-SiC growth on hexagonal SiC substrates.

Spatial Non-Uniform Hot Carrier Luminescence From 4H-SiC p-i-n Avalanche Photodiodes

4H-SiC avalanche photodiodes (APDs) working in Geiger mode are promising devices for ultra-weak ultraviolet light detection. In this letter, the degree of avalanche uniformity across device mesa of 4H-SiC p-i-n APDs is studied by imaging hot carrier luminescence pattern of the devices in avalanche regime. It is found that the luminescence emission from the APD under avalanche always first appears in the [ $\overline 1 \overline 1 20$ ] side of the top contact electrode. As over-bias increases, the luminescence pattern gradually extends toward the [ $11\overline 2 0$ ] direction and finally covers the whole device mesa. A physical model is proposed to explain the non-uniform avalanche phenomenon, in which the substrate off-orientation related carrier lateral drift would cause asymmetric hole accumulation and screening of junction electrical field along the [ $11\overline 2 0$ ] direction.

Interface of GaP/Si(001) and antiphase boundary facet-type determination

GaP/Si(001) virtual substrates are highly interesting for solar cells and optoelectronic device applications. While antiphase disorder at the resulting surface of the virtual substrate—after a few tens of nm GaP—can be suppressed, the structural and electronic properties of the actual GaP-to-Si interface and of the antiphase domains within the GaP are still of high importance. Here, we compare scanning tunneling microscopy data of the prepared Si(001) 2° off-oriented substrate with cross-sectional scanning tunneling microscopy data (XSTM) taken after GaP0.98N0.02/GaP growth. Besides regions where an intermixing of Si with GaP cannot be excluded, we also observe sections with a quite abrupt appearance. In addition, basic knowledge for use of contrast mechanisms occurring in XSTM experiments at antiphase boundaries will be established in order to understand their atomic structure. Thereby, we present a structural model for an entire antiphase domain cross section, including antiphase boundary facet-type determination. Furthermore, we find indications that the majority of the antiphase boundaries within this sample exhibit an equal number of so-called wrong bonds and that XSTM will allow to directly determine the electronic impact of the antiphase boundaries on its surroundings in the future.

Effect of substrate off-orientation on the characteristics of GaInP/AlGaInP single heterojunction solar cells

The effects of GaAs substrate off-orientation on GaInP/AlGaInP heterojunction solar cells were investigated. The performances of solar cells fabricated on 2° and 10° off GaAs substrates were compared. The short circuit current densities were 10.44 mA/cm2 for the 10° off sample, 7.15 mA/cm2 and 7.41 mA/cm2 for the 2° off samples, which showed 30% higher short-circuit current density for 10° off samples. Also, 30% higher external quantum efficiencies and smooth surface morphology were observed in the solar cell fabricated on the 10° off GaAs substrate. Secondary ion mass spectrometry depth profiles showed that the solar cells on 2° off substrates had a 20-times higher oxygen concentration than the solar cells on 10° off GaAs substrate in the n-GaAs/GaAs buffer layer. The 30% reduction for the solar cells on 2° substrates in short circuit current density (Jsc) was attributed to the higher oxygen concentration of the 2° off samples than the 10° off samples. I-V characteristics comparison between different front contact grid patterns was also performed for optimization of grid contacts. A 0.47 V bandgap-voltage offset, one of the device performance figures of merit to compare PV cells with different materials, was obtained.

An electromagnetic scanning mirror integrated with blazed grating and angle sensor for a near infrared micro spectrometer

This work presents an electromagnetic scanning mirror integrated with blazed grating and an angle sensor for a near infrared micro spectrometer. This device is fabricated on an aluminum coated 7.9° off-oriented (1 1 1) silicon substrate by utilizing the micro-electro-mechanical systems (MEMS) technology. The proposed MEMS electromagnetic scanning grating mirror not only provides high diffraction efficiency by integrating blazed grating, but also realizes the closed-loop control of the scanning angle by designing an angle sensor during the mirror scanning. Finally, in order to verify the effectiveness of this proposed device, the near infrared micro spectrometer is presented. The use of this MEMS electromagnetic scanning grating mirror allows the near infrared micro spectrometer to span a spectral range of 800 nm–1800 nm accurately. Based on this configuration, the near infrared micro spectrometer is extremely simple and only one single InGaAs photodetector is achieved, instead of a detector array.

(Invited) Growth, Defects and Doping of 3C-SiC on Hexagonal Polytypes

In recent years cubic silicon carbide (3C-SiC) has been regaining its importance among other SiC polytypes in development of various semiconductor device applications. Besides for active devices it can be used as a substrate for growth of high quality nitrides or epitaxial graphene layers. The quality of the latter greatly benefits from the absence of energy driven step bunching. The high electron mobility (~1000 cm2V-1s-1) and lower bandgap (~2.3eV) of 3C-SiC, compared to hexagonal SiC polytypes, enabled researchers to demonstrate the best channel mobility values (~300 cm2V-1s-1) among the SiC-based MOSFETs devices. The advantages of 3C-SiC for development of medium power devices have been recognized by the European Commission which is funding a collaborative research project ”CHALLENGE” (2017-2021) aiming at pushing 3C-SiC growth and device fabrication technologies closer to the market. There are also uprising innovative applications like intermediate band solar cells and photo electrochemical devices for water splitting which significantly benefit from the intrinsic 3C-SiC properties. Due to the lack of bulk 3C-SiC crystals, hetero-epitaxial growth on Si or hexagonal SiC substrates is the way used today to obtain 3C-SiC material with a size suitable for device fabrication. However, such 3C-SiC does not demonstrate the full potential of its intrinsic semiconductor properties due to a high density of defects, e.g. stacking faults, which are formed at the 3C-SiC/substrate interface. This problem is more pronounced in 3C-SiC grown on Si due to the large mismatch in lattice parameters and thermal expansion coefficients. Concomitantly, the majority of functioning devices, varying from MOSFETs to MEMS, have been demonstrated using such material. Therefore, it can be expected that mastering the growth and doping of 3С-SiC on hexagonal SiC substrates, especially providing high resistivity 3C-SiC material, would allow to demonstrate better performance of medium power devices. Although lattice and thermal matching between cubic and hexagonal SiC is not an issue, the 3C material quality on on-axis substrates is limited by the symmetry mismatch between SiC (0001) and 3C-SiC (111) , which induces rotational twinning and formation of double positioning boundaries (DPBs). Important fundamental problems on initial nucleation and defect formation have been already resolved and a solid background of knowledge has been delivered to developing of another 3C-SiC growth approach and that is to explore off-oriented hexagonal SiC substrates. In this talk we give a background of on-axis grown 3C-SiC and present results on growth of 3C-SiC crystals of superior structural quality using sublimation epitaxy. Bulk-like material with a thickness of about 1 mm and surface area of 10x10 mm2 can be reproducibly grown at temperatures below 2000oC in vacuum (10-5 mbar). The majority of growth studies were performed using 4H-SiC (0001) surfaces with the off-orientation of 4 degrees. In general, much higher density of steps on off-oriented surfaces, compared to on-axis, is a limitation in initiating 2D nucleation of 3C-SiC islands. However, under certain conditions a large facet/terrace can be formed at the edge of the substrate where an initial nucleation of 3C-SiC domains can be established. Upon growth progression, these domains enlarge laterally to cover the entire substrate surface with 3C-SiC. Such 3C-SiC substrates exhibit very high crystalline quality which was confirmed by HRXRD and LTPL analysis. The full width at half maximum (FWHM) value of ω rocking curves varied from 25 to 50 arc seconds. Typical defects in this type of growth are elongated domain boundaries which will be discussed. Unintentionally doped 3C-SiC layers with residual nitrogen concentration in a range of 1016 cm-3 exhibit resistivity of about 10-50 Ωcm. Such 3C-SiC substrates have been used for epitaxial growth of 3C-SiC and can be employed as seeds in sublimation bulk growth. We explored growth of intentionally B, Al, N and V doped 3C-SiC layers. The dopants were introduced by co-doping from the source material. We have demonstrated highly compensated 3C-SiC with resistivity close to 105 Ωcm range. I-V and C-V measurements of Schottky diodes fabricated on such material were used for the resistivity evaluation. SIMS and PL measurements have confirmed the presence of Vanadium. DLTS measurements are in progress for further identification of the deep levels. The growth issues related to dopants transfer as well as compensation mechanisms in high resistivity 3C-layers are discussed with special focus on V doped 3C-SiC material.

(Invited) Sublimation Growth of 3C-SiC: Status and Prospects

Cubic silicon carbide (3C-SiC) has been considered suitable for a number of device applications like MOSFETs, MEMS, solar cells, water splitting devices, and etc. However, the growth technologies for 3C-SiC are lagging behind its hexagonal counterparts (6H- and 4H-SiC). A primary reason is the lack of high quality 3C-SiC seeds which could be explored for the growth of bulk crystals or homoepitaxial layers. Although, some thermodynamic aspects on 3C-SiC stability should be accounted as well. During the initial developments of hexagonal SiC crystal growth techniques the hexagonal SiC seeds were grown by Acheson or Lely processes. Unfortunately, the 3C-SiC is rarely obtained using these processes. Therefore, it has to be heteroepitaxially grown on silicon or SiC substrates. In both cases there are still challenges in controlling the formation of structural defects at the 3C-SiC/substrate interface. A reproducible growth of 3C-SiC with a crystal size and crystalline quality similar to the hexagonal equivalents has not been demonstrated. Commonly, growth studies of 3C-SiC on SiC substrates by sublimation techniques were done using nominally on-axis hexagonal SiC surfaces. However, this approach has not succeeded in growth of crystals with reasonable structural quality. The main reason is the mismatch of symmetries between the SiC (0001) and 3C-SiC (111) which induces rotational twinning and formation of structural defects – double positioning boundaries (DPBs). Such defects could be avoided only if one 3C-SiC domain or several with the same orientation nucleate on the surface. In contrast to on-axis substrates, the off-orientated substrates have been a typical choice for the growth of homoepitaxial hexagonal SiC layers or bulk crystals. The off-oriented surfaces contain high density of steps which ensures reproduction of the substrate polytype. This has been considered by most of the researchers as an obstacle towards stable 3C-SiC growth. However, under certain conditions, off-oriented SiC substrates can be used to grow 3C-SiC with well controlled initial nucleation. In this paper we will present our recent results on the growth of thick (~1 mm) 3C-SiC layers on off-oriented SiC substrates using sublimation epitaxy. The design of graphite crucible was optimized using numerical simulations to obtain high polytype stability and reproducible growth of 3C-SiC at temperatures below 2000oC in vacuum (10-5 mbar). Based on our knowledge of the initial 3C-SiC nucleation on nominally on-axis and low off-axis surfaces we developed and optimized 3C-SiC growth approach using 4H-SiC (0001) surfaces with the off-orientation of 4 degrees. We will also present results on the growth of 3C-SiC on 6H- and 15R-SiC. The 3C-SiC layer grown using this approach pass through three interconnected growth stages which include formation of a large terrace/facet with an on-axis area at the edge of the sample, preferential nucleation of 3C-SiC domains on the large terrace, and their lateral enlargement along the step-flow direction. In order to obtain a single domain layers we have developed a two-step growth process and applied geometrical control using spacers, separating the source and the substrate, with different geometries. The HRXRD and LTPL analysis of 3C-SiC layers indicate high crystalline quality. The average value of the full width at half maximum (FWHM) of ω rocking curves is about 40 arcseconds. The LTPL spectra demonstrate well resolved near-band-edge features and lines associated with multiple bound-exciton complexes with up to four electron−hole pairs. The layers are usually unintentionally doped with nitrogen and exhibit resistivity of about 10-50 Ωcm. Furthermore, such layers were used as substrates for sublimation growth of homopeitaxial layers with intentional doping of B and V. The dopants were introduced by co-doping from the source material. Single domain 3C-SiC layers were used as seeds to explore the growth of bulk (thickness 4-5 mm) material by sublimation. The absence of DPBs allows us to analyze the development of a bulk crystal and the effect of other defects like stacking faults, secondary inclusions and threading defects on the crystalline quality of the bulk material. We will present our recent results and discuss further prospects for the growth of bulk 3C-SiC crystals.

Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates

We investigated the formation of structural defects in thick (∼1 mm) cubic silicon carbide (3C-SiC) layers grown on off-oriented 4H-SiC substrates via a lateral enlargement mechanism using different growth conditions. A two-step growth process based on this technique was developed, which provides a trade-off between the growth rate and the number of defects in the 3C-SiC layers. Moreover, we demonstrated that the two-step growth process combined with a geometrically controlled lateral enlargement mechanism allows the formation of a single 3C-SiC domain which enlarges and completely covers the substrate surface. High crystalline quality of the grown 3C-SiC layers is confirmed using high resolution X-ray diffraction and low temperature photoluminescence measurements.

Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates

We introduce a 3C-SiC growth concept on off-oriented 4H-SiC substrates using a sublimation epitaxial method. A growth model of 3C-SiC layer development via a controlled cubic polytype nucleation on ...

Role of SiC substrate polarity on the growth and properties of bulk AlN single crystals

Two symmetrically nonequivalent silicon carbide (SiC) substrate orientations, (0001) Si-terminated and \((000\overline{1} )\) C-terminated, were used in the physical vapour transport growth of bulk aluminium nitride (AlN) single crystals. The crystals grown on Si-faces always exhibit an Al-polar growth surface. AlN growth on \((000\overline{1} )\) C-terminated surfaces of the SiC substrates was performed to obtain N-polar growth surfaces. An abrupt interface was observed between the AlN crystal and the C-face substrate which is in contrast to the growth on Si-faces where hexagonally shaped SiC hillocks are formed. The growth on C-faces is usually dominated by multi-site nucleation. Applying similar supersaturation conditions that led to step-flow growth on Si-faces to the C-faces resulted in a spiral growth mode, even on highly off-oriented substrates. The obtained broad X-ray diffraction rocking curves of such samples (full-width at half-maximum ≈380 arcsec) indicate the presence of more misfit dislocations and significant misfit stress. In addition, polarity inversion is observed in C-face grown crystals. Though the structural properties of the crystals grown on C-face are inferior to that of the crystals grown on Si-face, the incorporation of unintentional Si impurity was found to be lower (<2 wt%).

Step Instability in Sublimation Epitaxy on Low Off-Axis 6H-SiC

The growth of homoepitaxial layers on off-oriented 6H-SiC substrates proceeds via step flow growth. Such epilayers can exhibit irregularities like step bunching, splicing or crossover of steps. The effects of the substrate off-orientation and growth temperature show an influence on formation of surface irregularities. The mean features seem to be given by the growth mode competition of two-dimensional growth to the step-flow growth.

Bulk AlN single crystal growth on foreign substrate and preparation of free-standing native seeds

Physical vapour transport growth of aluminium nitride (AlN) single crystals on silicon carbide (SiC) substrates has been optimised and crack-free, large-area, free-standing (0001) AlN wafers were prepared from the grown template crystals. 28 mm diameter single crystals without any polycrystalline surroundings were obtained. Different off-oriented substrates give rise to different growth modes. Sharp and symmetric line shapes of X-ray diffraction (XRD) rocking curves and high intense Raman phonon mode peaks prove high structural quality and homogeneity of the grown crystals. Full width at half maximum of the rocking curves is 72 arcsec for symmetric 00.2 reflection and 200 arcsec for asymmetric 10.3 reflection, representing a low screw as well as edge type threading dislocations. Wet chemical etching results also confirm the above XRD results and the estimated etch pit density is as low as 2–5 × 105 cm−2. The growth surfaces of all the crystals show only Al-polarity as inferred by the etching analysis. The concentration of silicon and carbon impurities incorporated from the SiC substrate decreases with the growth length of the AlN crystals. These impurities might play a decisive role in determining the optical properties of the crystal and be responsible for the absence of near-bandgap excitonic luminescence. Confocal Raman spectra show only the phonon modes allowed by the selection rules for the measured symmetry. The observed E2(high) phonon mode frequency very closely matches the reported stress-free phonon frequency of AlN. This work demonstrates that AlN templates prepared on SiC as a foreign substrate can be used as native seeds for the growth of further homo-epitaxial layers and crystalline boules.

In situ grown Ge in an arsenic-free environment for GaAs/Ge/GaAs heterostructures on off-oriented (100) GaAs substrates using molecular beam epitaxy

High-quality epitaxial Ge layers for GaAs/Ge/GaAs heterostructures were grown in situ in an arsenic-free environment on (100) off-oriented GaAs substrates using two separate molecular beam epitaxy (MBE) chambers, connected via vacuum transfer chamber. The structural, morphological, and band offset properties of these heterostructures are investigated. Reflection high energy electron diffraction studies exhibited (2 × 2) Ge surface reconstruction after the growth at 450 °C and also revealed a smooth surface for the growth of GaAs on Ge. High-resolution triple crystal x-ray rocking curve demonstrated high-quality Ge epilayer as well as GaAs/Ge/(001)GaAs heterostructures by observing Pendellösung oscillations and that the Ge epilayer is pseudomorphic. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of ∼0.45 nm and room temperature photoluminescence spectroscopy exhibited direct bandgap emission at 1583 nm. Dynamic secondary ion mass spectrometry depth profiles of Ga, As, and Ge display a low value of Ga, As, and Ge intermixing at the Ge/GaAs interface and a transition between Ge/GaAs of less than 15 nm. The valence band offset at the upper GaAs/Ge-(2 × 2) and bottom Ge/(001)GaAs-(2 × 4) heterointerface of GaAs/Ge/GaAs double heterostructure is about 0.20 eV and 0.40 eV, respectively. Thus, the high-quality heterointerface and band offset for carrier confinement in MBE grown GaAs/Ge/GaAs heterostructures offer a promising candidate for Ge-based p-channel high-hole mobility quantum well field effect transistors.

On Stabilization of 3C-SiC Using Low Off-Axis 6H-SiC Substrates

Heteroepitaxial growth of 3C-SiC on 0.8 and 1.2 degree off-oriented 6H-SiC substrates was studied using a sublimation growth process. The 3C-SiC layers were grown at high growth rates with layer thickness up to 300 µm. The formation and the quality of 3C-SiC are influenced by the off-orientation of the substrate, the growth temperature (studied temperature range from 1750 °C to 1850°C), and the growth ambient (vacuum at 5*10-5 mbar and nitrogen at 5*10-1 mbar). The largest domains of 3C-SiC and the lowest number of double positioning boundaries were grown using nitrogen ambient and the highest growth temperature. The combined use of low off-axis substrate and high growth rate is a potential method to obtain material with bulk properties.

Direct observation of basal-plane to threading-edge dislocation conversion in 4H-SiC epitaxy

The propagation behavior of basal plane dislocations from off-oriented 4H-SiC substrates into homoepitaxial layers has been investigated using transmission electron microscopy (TEM), secondary electron microscopy (SEM), and chemical etching. Cross-sectional TEM shows that basal plane dislocations in the substrate are dissociated into pairs of partial dislocations separated by a stacking fault with a width of about 40 nm. Near the substrate/epilayer interface, where most of the basal plane dislocations convert to threading edge dislocations, the two partials constrict before converting. Threading edge segments are inclined by about 20° from the c-axis toward the down-step direction. It is concluded that the critical and limiting step of the dislocation conversion process is constriction of the dissociated partials. Growth surface morphology at the emergence point of the basal plane dislocation was imaged using SEM and is thought to play an important role in the constriction.

X-ray Study of Step Induced Lateral Correlation Lengths in Thin AlGaN Nucleation Layers

A 15 nm thick high temperature AlGaN nucleation layer was grown on a slightly off-oriented c-plane sapphire substrate by metal–organic vapor phase epitaxy. The evaluation of this layer by high resolution X-ray diffraction yields a nucleation with a threefold distribution of the rotational disorder within about 4° in the ω-scan at the in-plane AlGaN(1100) reflection, whereas the ω-scan at the symmetric AlGaN(0002) reflection exhibits a very narrow correlation peak. In addition, two weaker signals could be determined in the symmetric ω-scan. The positions of these minor maxima with respect to the correlation peak depend on the azimuth angle of the incident X-ray beam. Based on the determined off-orientation angle and lateral coherence lengths the phenomenon is explained in terms of a stepped sapphire surface morphology.

Epitaxial growth on 4H-SiC by TCS as a silicon precursor

Epitaxial growth on n-type 4H-SiC 8° off-oriented substrates with a size of 10 × 10 mm2 at different temperatures with various gas flow rates has been performed in a horizontal hot wall CVD reactor, using trichlorosilane (TCS) as a silicon precursor source together with ethylene as a carbon precursor source. The growth rate reached 23 μm/h and the optimal epilayer was obtained at 1600 °C with a TCS flow rate of 12 sccm in C/Si of 0.42, which has a good surface morphology with a low RMS of 0.64 nm in an area of 10 × 10 μm2. The homoepitaxial layer was obtained at 1500 °C with low growth rate (< 5 μm/h) and the 3C-SiC epilayers were obtained at 1650 °C with a growth rate of 60–70 μm/h. It is estimated that the structural properties of the epilayers have a relationship with the growth temperature and growth rate. Silicon droplets with different sizes are observed on the surface of the homoepitaxial layer in a low C/Si ratio of 0.32.

Large-Area Homoepitaxial Growth of Low-Doped Thick Epilayers for Power Devices with V&lt;sub&gt;BR&lt;/sub&gt; &gt; 4 kV

In this paper we present results on the growth of low-doped thick epitaxial layers on 4° off-oriented 4H-SiC using a commercially available hot-wall multi-wafer CVD system. For the first time we show results of a low-doped full-loaded 73” run on 4° off-oriented substrates with a layer thickness of more than 70 µm. The target doping concentration of 1.2×1015 cm-3 is suitable for blocking voltages &gt; 6 kV. Results on doping, thickness and wafer-to-wafer homogeneities are shown. The surface quality of the grown layers was characterized by AFM. The density of different types of dislocations was determined by Defect Selective Etching.

Suppression of domain formation in GaN layers grown on Ge(1 1 1)

Heteroepitaxial growth of GaN on Ge(1 1 1) by molecular beam epitaxy has previously been reported to be feasible. However, structural characterization revealed that these GaN layers consisted of misoriented domains. In this work, it is shown that the formation of domains can be suppressed by increasing the substrate temperature, decreasing the nitrogen flux or increasing the surface step density by using off-oriented substrates. Hereby, the step flow growth is enhanced with respect to 2D nucleation. The suppression of domains significantly improves the crystal quality of the GaN layer. For 47 nm of GaN a (0 0 0 2) and (1 0 1¯ 2) ω FWHM value of, respectively, 408 and 935 arcsec is obtained.