Vladimir Ivantsov

Characterization of 2.5 Inch Diameter Bulk GaN Grown from Melt-Solution

GaN bulk crystals up to 2.5-inch diameter were grown from melt-solution. Properties of these crystals were investigated using Auger electron spectroscopy, X-ray diffraction and photoluminescence.

Accumulation of Background Impurities in Hydride Vapor Phase Epitaxy Grown GaN Layers

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.

Morphological, electrical, and optical properties of InN grown by hydride vapor phase epitaxy on sapphire and template substrates

We report studies of the morphological, electrical, and optical properties of InN grown by hydride vapor phase epitaxy. The layers have been grown on c-plane sapphire substrates and epitaxial GaN, Al0.7Ga0.3N, and AlN templates grown on sapphire. InN properties are found to depend on template type with improvement of crystal structure in the template substrate order AlN→AlGaN→GaN. X-ray studies reveal InN layers grown on template substrates to be relaxed with lattice constants a=3.542A and c=5.716A. The Raman spectra and optical gaps of the InN layers, vary with free-carrier concentration in agreement with previous studies. We obtain a value of 2.5±0.2 for the index of refraction of InN.

P-type GaN epitaxial layers and AlGaN/GaN heterostructures with high hole concentration and mobility grown by HVPE

In this paper we report p-GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg or Zn impurities were used for doping. Layer thickness ranged from 2 to 5 microns. For both impurities, as-grown GaN layers had p-type conductivity. Concentration NA-ND was varied from 1016 to 1018 cm−3. An annealing procedure at 750°C in argon ambient typically increased the concentration NA-ND in 1.5–3.5 times. For Mg doped GaN layers, room temperature hole mobility of 80 cm2V−1s−1 was measured by conventional Van Der Pau Hall effect technique for material having hole concentration of about 1x1018 cm−3. Initial results on highly electrically conducting p-type AlGaN/GaN heterostructures doped with Zn are also reported.

A Comparative Study of Dislocations in HVPE GaN Layers by High-Resolution X-Ray Diffraction and Selective Wet Etching

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.

InN Nano Rods and Epitaxial Layers Grown by HVPE on Sapphire Substrates and GaN, AlGaN, AlN Templates

ABSTRACT This paper contains results on InN growth by Hydride Vapor Phase Epitaxy (HVPE) on various substrates including sapphire, GaN/sapphire, AlGaN/sapphire, and AlN/sapphire templates. The growth processes were carried out at atmospheric pressure in a hot wall reactor in the temperature range from 500 to 650oC. Arrays of nano-crystalline InN rods with various shapes were grown directly on sapphire substrates. Continuous InN layers were grown on GaN/sapphire, AlN/sapphire and AlGaN/sapphire template substrates. X-ray diffraction rocking curves for the (00.2) InN reflection exhibit the full width at half maximum (FWHM) as narrow as 0.075 deg. for the nano-rods and 0.128 deg. for the continuous layers grown on GaN/sapphire templates. INTRODUCTION Group III nitride compounds using InGaN-based active regions have attracted much attention as structures for short wavelength emitters operated in visible spectral range. Ability to grow high-quality thick InN-based active layers thought to be a way for further increasing the light emitters efficiency. Hydride vapor phase epitaxy (HVPE) is well-known method to produce both thick low-defect GaN, AlGaN, AlN templates and free-standing GaN substrates for nitride device fabrication. One of the major technical issues in the development of InN materials is low dissociation temperature and high dissociation pressure of InN. Results of InN and InGaN growth by HVPE are limited. First experiments have been reported more than 25 years ago when InN layers were grown using reaction between ammonia and InCl

Thick AlN layers grown by HVPE on sapphire substrates

ABSTRACT Thick low defect AlN and AlGaN layers grown on ultra violet (UV) transparent substrates are considered as promising substrate materials for the UV light emitters and detectors. Electrically insulating thick AlN layers may serve as the substrates for AlGaN/GaN-based high power high electron mobility transistors (HEMTs). In this paper we report on crack-free up to 20 µm thick AlN layers grown by stress control HVPE on 2-inch sapphire substrates. As-grown surface had a characteristic pyramidal morphology. Being t hick enough, AlN layers can be polished to improve surface roughness. The minimum full width at half maximum (FWHM) values of AlN ω-scan x-ray (00.2) and (10.2) rocking curves was about 500 and 1000 arcsec, respectively. The XRD analysis was applied for the threading dislocation density evaluation in grown AlN layer. Screw dislocation density was found to be (3-7)x10 8 cm -2 for the layers from 3 to 12 µm thick. INTRODUCTION Hydride vapour phase epitaxy (HVPE) is known to produce low defect GaN substrate materials for electronic and optoelectronic GaN-based devices. High quality HVPE grown GaN layers and free-standing material have been recently demonstrated by several research teams as the substrates for GaN-based power devices [1], high-frequency transistors [2], and blue lasers [3]. However, GaN is not optically transparent in a UV spectral region for wavelengths shorter than 360 nm and wider band gap material are needed for deep UV applications. Due to large band gap (6.2 eV), high thermal conductivity (3.3 W/cm-K) and close thermal and lattice match to AlGaN layers, AlN is promising substrate material for advanced high power UV emitting devices (LEDs and LDs), UV detectors, ultra high power high frequency electronic devices (AlGaN/GaN HEMTs). However, bulk AlN substrates of required size (2-inch diameter and larger) are not available. One way to get over this issue is to fabricate AlN template substrates comprising thick low defect AlN layer grown on a foreign substrate. The main technical challenge here is to minimize stresses in such template substrate and to avoid cracking of the AlN layer. Recently we have reported on stress control HVPE technology to grow thick (>50µm) crack-free AlN layers on SiC substrates [4]. In this paper we report on crack-free AlN layers up to 20 µm thick grown by HVPE on 2-inch sapphire substrates. Results of 3-15 µm thick layers characterization are discussed.

AlGaN materials for semiconductor sensors and emitters in 200- to 365-nm range

In this paper we report on the fabrication and characterization of GaN, AlGaN, and AlN layers grown by hydride vapor phase epitaxy (HVPE). The layers were grown on 2-inch and 4-inch sapphire and 2-inch silicon carbide substrates. Thickness of the GaN layers was varied from 2 to 80 microns. Surface roughness, Rms, for the smoothest GaN layers was less than 0.5 nm, as measured by AFM using 10 μm x 10 μm scans. Background Nd-Na concentration for undoped GaN layers was less than 1x1016 cm-3. For n-type GaN layers doped with Si, concentration Nd-Na was controlled from 1016 to 1019 cm-3. P-type GaN layers were fabricated using Mg doping with concentration Na-Nd ranging from 4x1016 to 3x1018 cm-3, for various samples. Zn doping also resulted in p-type GaN formation with concnetration ND-NA in the 1017 cm-3 range. UV transmission, photoluminescence, and crystal structure of AlGaN layers with AlN concentration up to 85 mole.% were studied. Dependence of optical band gap on AlGaN alloy composition was measured for the whole composition range. Thick (up to 75 microns) crack-free AlN layers were grown on SiC substrates. Etch pit density for such thick AlN layers was in the 107 cm-2 range.