Co-doping with manganese and carbon was performed in gallium nitride (GaN) grown by halide vapor phase epitaxy (HVPE). The crystallized material was examined in terms of its structural, optical, and electrical properties. Basing on Raman and photoluminescence spectra of the samples it will be presented that in the GaN:Mn,C crystals Mn is in a different electrical state (Mn^(3+/4+)) in comparison to Mn in GaN:Mn (Mn^(2+/3+)). This change is due to the presence of carbon, which forces manganese to change the oxidation state. This phenomenon will be analyzed and confirmed by the examination of the electrical properties of obtained crystals.
In this paper we would like to report the recent progress in basic ammonothermal GaN crystal growth. Growth on ammonothermal GaN seeds is presented. Structural properties of the seeds are shown and discussed. A new shape of seed crystals is proposed. It allows to eliminate the appearance of cracks in the growing GaN. The unwanted lateral growth is restricted and controlled. A higher growth rate, both in lateral and vertical directions, is obtained. Generally, the high structural quality of native seeds is maintained. In case of crystallization in lateral directions the structural quality of the seeds can even be improved. The influence of the crystallization run parameters, growth direction and configuration on the structural quality of the obtained GaN will be discussed.
Recent progress in bulk GaN growth technology will be presented. New results of basic ammonothermal GaN crystallization and halide vapor phase epitaxy (HVPE) of GaN will be shown and analyzed. The advantages, disadvantages and challenges of both methods will be discussed. An influence of lateral growth on critical thicknesses and structural quality of crystallized GaN layers by both methods will be demonstrated. Reduction of lateral crystallization and growth only in one crystallographic direction will be shown.
A review on doping with acceptors of pure and structurally perfect HVPE-GaN single crystals grown on the native Ammono-GaN seeds will be described in this paper. Solid iron (Fe), manganese (Mn), magnesium (Mg) or methane (CH4, precursor of carbon) were used as dopant source to crystallize semi-insulating HVPE-GaN. Carbon-doped GaN was highly resistive at room temperature (exceeding 1×108 Ω.cm at 296 K) and became p-type at high temperature. Activation energy of 1 eV was an experimental confirmation of theoretical calculations for CN (deep acceptor). Doping with manganese also led to very high values of resistivity. In this case the activation energy was close to 1.8 eV. Resistivity of GaN with Mn concentration of 1017 cm-3 exceeded 108 Ω.cm at room temperature. Hall measurements revealed n-type conductivity at high temperature. Co-doping of HVPE-GaN with Mn and Mg led to highly resistive material at room temperature (exceeding 1×108 Ω.cm) and p-type at high temperature. The activation energy was 1.2 eV above the maximum of the valence band. GaN doped with Fe was also highly resistive at room temperature (3×107 Ω.cm with free electron concentration of 5×108 cm-3). It showed n-type properties at high temperature and activation energy of around 0.6 eV below the minimum of the conduction band. Structural, optical, and electrical properties of the resulting semi-insulating HVPE-GaN will be examined, presented, and compared in this paper.
HVPE can be used for growing thin, up to 200 µm, GaN layers of high purity and low free carrier concentration. Deposition of such material on conductive n-type GaN seeds results in a structure which is the basis of some vertically operating electronic devices. It should be stressed that thickness of this GaN with low free carrier concentration influences the breakdown voltage of the devices. Therefore, HVPE becomes the main epitaxial technology for crystallizing such layers. The method allows to crystalize GaN with a relatively high growth rate of about 100 µm/h. It makes this technology crucial for preparing transistor structures with breakdown voltage higher than a few or several kV. The main goal of this paper is to investigate implantation of beryllium (Be) acceptors into thin (10-100 µm) unintentionally doped layers of GaN crystallized by HVPE on native seeds. A nitride structure comprising of an n-type layer of low free carrier concentration with implanted regions with p-type conductivity or semi-insulating and a highly conductive n-type substrate will be obtained. Basic parameters of HVPE-GaN growth processes (reagent flows, growth temperature) as well as parameters of ion implantation will be determined. Post-implantation damage, which occurs in implanted layers, will be removed by high-temperature (1400-1480°C) annealing at high nitrogen pressure (1 GPa). Basic structural, optical, and electrical parameters of implanted and annealed GaN will be investigated. The samples will be characterized prior to and after ion implantation.
The main objective of this paper is crystallization of AlGaN by HVPE method. Source of Al will be metallic aluminum. Hydrochloride flow will be set above the Al source at temperature of 500ºC and as a result of reaction AlCl will form. Aluminum monochloride will be transported to the growth zone of AlGaN. The following growth parameters will be established and analyzed: i/ growth temperature, ii/ flows of gas reagents (HCl above gallium, HCl above metallic Al, ammonia), iii/ carrier gas composition (N2 or nonreactive gas). Determining proper parameters should result in a stable growth of HVPE-AlGaN layers with a desired composition of aluminum (Al content from 1 to 25%). Distribution of aluminum will be uniform in the grown layers. HVPE-AlGaN will be thick up to 100 µm. Their diameter will depend on the used seed – up to 2-inch. Structural, optical and electrical properties of HVPE-AlGaN will be examined and presented in this paper.
The main objective of this paper is crystallization of semi-insulating material with resistivity ~109 Ωcm in temperature range between 296 K and 1000 K. No free carriers should be activated at elevated temperature. Source of Mn dopant will be metallic manganese. Hydrochloride flow will be set above the Mn source and as a result of reaction MnCl2 will form. Manganese dichloride will be transported to the growth zone of GaN. The following growth parameters will be established and analyzed: i/ growth temperature, ii/ flows of gas reagents (HCl above gallium, HCl above metallic Mn, ammonia), iii/ carrier gas composition (N2, H2, mixture of N2 + H2, or nonreactive gas), iv/ temperature of metallic Mn source. Determining proper parameters should result in a stable growth of HVPE-GaN:Mn crystals with a desired morphology (hillocks). Distribution of manganese dopant will be uniform in the grown layer. HVPE-GaN:Mn will be thicker than 1 mm. Their diameter will depend on the used seed – up to 2-inch. The layers will be removed from the seeds by slicing procedure and as a result free-standing HVPE-GaN:Mn will be obtained. Structural, optical and electrical properties of this material will be examined and presented.
Advanced Substrates consist of a 200-nm-thick GaN layer bonded to a handler wafer. The thin layer is separated from source material by Smart CutTM technology. GaN on Sapphire Advanced Substrates were used as seeds in HVPE-GaN growth. Unintentionally doped and silicon-doped GaN layers were crystallized. Free-standing HVPE-GaN was characterized by X-ray diffraction, defect selective etching, photo-etching, Hall method, Raman spectroscopy, and secondary ion mass spectrometry. The results were compared to HVPE-GaN grown on standard MOCVD-GaN/sapphire templates.
In this article homoepitaxial HVPE-GaN growth in directions other than [0001] is described. Three crystallization runs on (11-20), (10-10), (20-21), and (20-2-1) seeds were performed. In each experiment a different carrier gas was used: N2, H2, and a 50% mixture of N2 and H2. Other conditions remained constant. An influence of the growth direction and carrier gas on growth rate and properties (morphology, structural quality, and free carrier concentration determined by Raman spectroscopy) of obtained crystals was investigated and discussed in details. For all crystallographic directions a lower growth rate was determined with hydrogen used as the carrier gas. Also, the highest level of dopants was observed for crystals grown under hydrogen. A possibility to obtain highly conductive GaN layers of high quality without an intentional doping is demonstrated.
HVPE crystallization on ammonothermaly grown GaN crystals (A-GaN) is described. Preparation of the (0001) surface of the A-GaN crystals to the epi-ready state is presented. The HVPE initial growth conditions are determined and demonstrated. An influence of a thickness and a free carrier concentration in the initial substrate on quality and mode of growth by the HVPE is examined. Smooth GaN layers of excellent crystalline quality, without cracks, and with low dislocation density are obtained.
Role and influence of impurities like: oxygen, indium and magnesium, on GaN crystals grown from liquid solution under high nitrogen pressure in multi-feed-seed configuration is shown. The properties of differently doped GaN crystals are presented. The crystallization method and the technology based on it (for obtaining high quality GaN substrates) are described in details. Some electronic and optoelectronic devices built on those GaN substrates are demonstrated.
Violet and blue Laser diodes, as well as highly efficient high-power Light Emitting Diodes (including any UV
emitters) can be constructed using low-dislocation-density freestanding GaN substrates, either produced as thick
HVPE layers on foreign substrates, or using direct methods of crystallization as ammonothermal one or high
pressure growth from the nitrogen solution in gallium. This paper shows some of the most most important issues
concerning application of such substrates. The first issue is the choice of the substrate thickness influencing the
accommodation of strain, cracking and bowing of the samples. In this point, a new way of prestressing the
substrate by lateral patterning will be presented. The second issue is the surface preparation either by mechanical
polishing and reactive ion etching, or mechano-chemical polishing, in particular, a distribution of defects
revealed by chemical etching will be discussed. Finally, the problem of substrate misorientation influencing the
further morphology and indium incorporation into InGaN quantum wells will be shown. For higher
misorientation of the substrates, the incorporation of indium decreases , but at the same time, the fluctuations of
indium increase giving blue-shifted, weaker and broader photoluminescence peaks.
In this work the results of high pressure solution growth of GaN on various patterned substrates are presented. The growth on GaN/sapphire substrates patterned in GaN parallel stripes and with SixNy and Mo masks between stripes is studied and analyzed. The results are compared with the growth on patterned substrates without any mask, thus with a bare sapphire between stripes. The usefulness of tungsten and iridium for masking is also determined. The HVPE free standing GaN substrates with high stripes, up to 10 mm, are examined in details. The stripes growth modes are shown and described.
Growth of GaN under pressure from solution in gallium results in almost dislocation free plate-like crystals but with size limited to app. 1-2 cm (lateral) and 100 μm (thickness) or up to about 1cm long needles. Deposition of GaN by HVPE on the pressure grown seeds allows stable crystallization (in terms of flatness of the crystallization front and uniformity of the new grown material) at a rate of about 100 μm/h on both types of seed crystals. However, in the thick GaN crystals grown on almost dislocation free plate-like substrates quite a high number of dislocations appears if the crystal thickness exceeds certain critical value. Since the critical thickness for defect generation is of the order of 100 μm, almost dislocation free layers (density below 104 cm-2) thinner than 100 μm can be grown. The most obvious further step is removing the substrate and continuation of the HVPE deposition on the free standing low dislocation density layer of sub-critical thickness. The pressure grown substrates were removed by mechanical polishing or conductivity sensitive electrochemical etching (for strongly n-type substrates). Then the HVPE low dislocation density GaN 1platelets were used as substrates for the growth of a few mm thick bulk GaN crystals. The crystals were characterized by defect selective etching of both polar (0001) and non-polar (10 -10) surfaces to check presence and distribution of structural defects. The X-ray measurements allowed concluding about character of strain and deformation in high pressure GaN-HVPE GaN system.
In this paper we discuss the applicability of high-pressure grown bulk GaN crystals as substrates for device oriented MOVPE homoepitaxy. First, we fabricated light emitting diodes as a step towards realization of our target device: a blue light emitting laser diode. Our homoepitaxialy grown LEDs are characterized by excellent electrical characteristics and very satisfactory optical properties. Building on the experience gained during this first stage of our research we have been able to fabricate pulse current operated laser diodes emitting light at a wavelength between 397 and 430 nm. We believe that this fast progress clearly demonstrates the usefulness of bulk GaN substrates for optoelectronic devices, especially for high power laser diodes.
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