A spontaneous change of growth orientation from polar c to nonpolar a-plane during hydride vapor-phase epitaxy of GaN on c-plane sapphire substrates was examined by X-ray diffraction 20-omega and omega-scans and pole figures as well as by scanning electron microscopy. The effect was observed in epitaxial layers grown on the substrates without a buffer layer. It was found that the advancement of the transition to the a-plane did not comply with the gradual transformation usual for the geometric selection but followed instead with the abrupt change from one orientation to another, finalizing above the substrate surface. Pole figures revealed twinning in the epilayers. This twinning, together with the observed influence of the substrate treatment on the result of epitaxy, favored the model that put forward the faceting of the sapphire surface, especially faceting with the r-facets, as the main reason for the reorientation effect. The discussion of the model unwrapped the importance of r-faceting not just for the growth on the c-plane sapphire but for the growth on the m-and a-planes also.

We report on accumulation of background Si and O impurities measured by secondary ion mass spectrometry (SIMS) at the sub-interfaces in undoped, Zn- and Mg-doped multi-layer GaN structures grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates with growth interruptions. The impurities accumulation is attributed to reaction of ammonia with the rector quartz ware during the growth interruptions. Because of this effect, HVPE-grown GaN layers had excessive Si and O concentration on the surface that may hamper forming of ohmic contacts especially in the case of p-type layers and may complicate homo-epitaxial growth of a device structure.

It has been shown during the present study that the E-etching at elevated temperatures can be adopted for the dislocation etching in hydride vapor-phase epitaxy (HVPE) GaN layers. It has been found that the X-ray diffraction (XRD) evaluation of the dislocation density in the thicker than 6 μm epilayers using conventional Williamson-Hall plots and Dunn-Koch equation is in an excellent agreement with the results of the elevated-temperature E-etching. The dislocation distribution measured for 2-inch GaN-on-sapphire substrate suggests strongly the influence of the inelastic thermal stresses on the formation of the final dislocation pattern in the epilayer.

The employment of more than 10μm thick AlN epilayers on SiC substrates for AlGaN/GaN high-electron-mobility transistors (HEMTs) substantially raises their performance in high-power energy-efficient amplifiers for 4G wireless mobile stations. In this paper, structural properties and surface morphology of thick AlN epilayers deposited by hydride vapor phase epitaxy (HVPE) on off-axis conductive 6H-SiC substrates are reported. The epilayers were examined in detail by high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), Nomarski differential interference contrast (DIC), scanning electron microscopy (SEM), and selective wet chemical etching. At optimal substrate preparation and growth conditions, a full width at half-maximum (FWHM) of the XRD rocking curve (RC) for the symmetric (00.2) reflex was very close to that of the substrate (less than 40arcsec) suggesting low screw dislocation density in the epilayer (∼106cm−2) and small in-plane tilt misorientation. Reciprocal space mapping around asymmetric reflexes and measured lattice parameters indicated a fully relaxed state of the epilayers. The unit-cell-high stepped areas of the epilayers with 0.5nm root mean square (RMS) roughness over 1×1μm2 scan were alternated with step-bunching instabilities up to 350nm in height. Low warp of the substrates makes them suitable for precise epitaxy of HEMT structures.

Results for long-wavelength emitters are presented for semi-polar InGaN/AlGaN/GaN heterostructures grown on GaN(1122)/m-sapphire templates by metalorganic chemical vapor deposition. The semi-polar GaN layers were 10 to 25 mu m thick and grown by HVPE on sapphire substrates. X-ray diffraction measurements indicate high crystallographic quality that approaches that of GaN(0001) layers on sapphire. Growth studies on the semi-polar GaN templates established the high efficiency of indium incorporation into InGaN layers, with a wide growth-temperature window up to 800 degrees C for green light emitting structures. Basic LEDs were fabricated with peak emission up to 527 nm wavelength. Further growth studies established conditions for growing reasonably smooth, undoped InGaN/GaN laser heterostructures suitable for optical pumping. Optically-pumped lasing was achieved at wavelengths from 400 nm up to 500 nm. The results demonstrate the viability of semi-polar GaN(1122) on sapphire templates for long-wavelength nitride laser diodes. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper reports structural characterization of thick $(11\bar {2}2)$‐oriented GaN layers by means of XRD, TEM, and micro‐ CL. The semi‐polar $(11\bar {2}2)$ GaN layers were grown on m‐plane sapphire substrates by HVPE. Their structural quality improved with thickness. Threading dislocation density of 3 × 108 cm−2 and stacking faults density of 4 × 104 cm−1 were measured at the surface of 20 µm thick $(11\bar {2}2)$ GaN layers. The semi‐polar GaN layers were used as template substrates to grow InGaN/GaN MQW heterostructures by MOCVD that demonstrated optically pumped lasing at 500 nm wavelength. The results demonstrate the longest wavelength yet reported for a photo‐pumped laser on template substrates.

Results for long-wavelength emitters are presented for semi-polar InGaN/AlGaN/GaN heterostructures grown on GaN(1122)/m-sapphire templates by metalorganic chemical vapor deposition. The semi-polar GaN layers were 10 to 25 μm thick and grown by HVPE on sapphire substrates. X-ray diffraction measurements indicated high crystallographic quality that approaches that of GaN(0001) layers on sapphire. A comparison based on optical pumping experiments, low- and high-density excitation photoluminescence experiments, and atomic force microscopy is drawn between InGaN/GaN quantum well laser heterostructures grown by metalorganic vapor phase epitaxy either on either polar GaN(0001)/c-sapphire or on semi-polar GaN(1122)/m-sapphire. C-plane InGaN/GaN/sapphire structures exhibited low threshold pump power densities < 500 kW/cm2 for emission wavelengths up to 450 nm. For laser structures beyond 450 nm the threshold pump power density rapidly increased resulting in a maximum lasing wavelength of 460 nm. Semipolar InGaN/GaN(1122)/m-sapphire structures showed a factor of 2-4 higher threshold pump power densities at wavelengths below 440 nm which is partly due to lower crystalline perfection of the semi-polar GaN/sapphire templates. However, at longer wavelengths > 460 nm the threshold power density for lasing of semi-polar heterostructures is less than that for c-plane heterostructures which enabled rapid progress to demonstration of lasing at 500 nm wavelength on semi-polar heterostructures. The absence of V-type defects in semi-polar, long-wavelength InGaN/GaN structures which are usually present in long-wavelength c-plane InGaN/GaN structures is attributed to this phenomenon.

Semipolar GaN layers were grown on m-plane sapphire substrates by HVPE. Insertion of AlxGa1–xN (x ∼ 0.1-0.6) layer in-between m-plane sapphire substrate and GaN layer promoted to improve crystalline quality and to grow of semipolar (11-22) plane GaN layers. X-ray diffraction (11-22) ω-scan rocking curve FWHM of 298 arcsec was measured for a 30 μm thick (11-22) GaN layer. Depending on growth conditions, m-plane GaN layer having micro-crystallites of other orientations (mainly of (11-24) plane GaN layer) was also grown. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydride vapour phase epitaxy (HVPE) is known as fast deposition method to produce both free-standing GaN substrate materials and thick low-defect GaN on 2-inch sapphire and AlN layers on 2-inch sapphire and conductive silicon carbide (SiC) substrates. These substrate materials of 2-inch size are available as commercial product. In this paper, we extend the HVPE abilities to new fields including up to 23 mu m thick crack-free AlN layers growth on 3-inch and 100-mm SiC substrates (AlN/SiC template substrates) and up to 125 mu m thick GaN layers grown on 3-inch sapphire (GaN/sapphire template substrates). For 21-23 mu m thick AlN layers grown on 100-mm SiC substrates, the X-ray rocking curve FWHM was ranged from 200 to 300 arc sec and from 600 to 800 arc sec for the (00.2) and the (10.2) AlN reflections, respectively. For 115-125 mu m thick GaN layers, the X-ray FWHM values were 120-150 arcsec and 200-230arc sec for the (00.2) and the (10.2) GaN reflections, respectively, that corresponds screw dislocation density of (3-5)x10(7) cm(-2) evaluated based on XRD data. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this paper we report - on first InGaN-based light emitting structures grown by hydride vapour phase epitaxy (HVPE). InGaN layers and multi layer InGaN/InGaN epitaxial structures were grown on GaN/sapphire template substrates and characterized, InN content in the InGaN layers was varied from 5 to 35 mol. %. Thickness of InGaN layers was controlled from 10 nm to 2 microns. Density of treading dislocations in the InGaN layers was estimated to be in the 109 cm(-2) range. X-ray diffraction measurements and transmission electron microscopy data confirmed a formation of InGaN/InGaN superlattice structures. Light emitting diode epitaxial wafers were fabricated by HVPE deposition of n-type InGaN layers and multi layer structures on p-type GaN template substrates. Depending on InN content in the InGAN light emitting regions, peak electroluminescence wavelength varied from 450 to 510 nm. Results of material characterization are reported. Advantages of the proposed upside down LED configuration and future applications of HVPE to grow InGaN layers and structures are discussed. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on the properties of high quality HVPE InN and on successful subsequent MBE growth of InN layers with improved, characteristics on HVPE InN template substrates. InN layers were grown by HVPE on GaN/sapphire HVPE templates. The (00.2) XRD rocking-curve of the best InN layer (RC) had the FWHM of about 375 arc see, being the narrowest XRD RCs ever reported for HVPE InN. Transmission Electron Microscopy (TEM) revealed that at the GaN/InN interface, the threading dislocations that come from GaN were transmitted into the InN layer. We estimated the dislocation density in HVPE grown InN to be in the low 10(9) cm(-2) range. Reflection high energy electron diffraction (RHEED) confirmed monocrystalline structure of the InN layers surfaced layers photoluminescence (PL) showed edge emission, around 0.8 eV. Hall measured free electron concentration was in the range of 10(19) -10(20) cm(-3) and electron mobility was similar to 200 cm(3)/V s. MBE growth of InN was performed on the HVPE grown InN template substrate demonstrating the improvement of material quality in the case of homo-epitaxial growth of InN. Demonstration of the high quality HYPE InN materials opens a new way for InN substrate development.

A variety of new results on HVPE growth of group III nitride layers and heterostructures are described. Crack free from 10 to 30 mu m thick AlN layers were grown on 100-mm SiC substrates. Bowing of the AlN/SiC wafers was controlled below 10 microns. Low growth rate HVPE with deposition rate below 10 nm/min was demonstrated for GaN, AlN, and AlGaN. This process resulted in the first HVPE grown multi-quantum wells (MQWs) and superlattices. P-type as-grown GaN < Mg > layers with acceptor concentrations up to 3x10(19) cm(-3) were demonstrated. InGaN layers from 0.002 to 2 mu m thick were grown by HVPE for the whole composition range using c-plane GaN/sapphire template substrates. Non-polar InGaN layers were grown on a-GaN/r-sapphire templates and m-plane GaN bulk substrates. Blue and green all-HVPE LEDs were made utilizing InGaN MQWs grown on p-GaN/sapphire templates.

In this paper we report 3-7 mu m thick p-GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg impurity was used for doping. As-grown GaN layers had p-type conductivity with concentration N-A-N-D up to 3x10(19) cm(-3). Mg atom concentration was varied from 10(17) to 10(20) cm(-3). Hydrogen concentration was about 10 times less than that for Mg, which may explain effective p-type doping for as-grown GaN layers. Micro-cathodoluminescence revealed a columnar-like structure of the GaN layers with a non-uniform distribution of material regions having dominant 362 nm or 430 nm luminescence. Use of these thick p-GaN layers to grow InGaN-based blue and green LEDs by the HVPE is demonstrated.