John A. Edmond

Thin film deposition and microelectronic and optoelectronic device fabrication and characterization in monocrystalline alpha and beta silicon carbide

The deposition of silicon carbide thin films and the associated technologies of impurity incorporation, etching, surface chemistry, and electrical contacts for fabrication of solid-state devices capable of operation at temperatures to 925 K are addressed. The results of several research programs in the United States, Japan and the Soviet Union, and the remaining challenges related to the development of silicon carbide for microelectronics are presented and discussed. It is concluded that the combination of alpha -SiC on alpha -SiC appears especially viable for device fabrication. In addition, considerable progress in the understanding of the surface science, ohmic and Schottky contacts, and dry etching have recently been made. The combination of these advances has allowed continual improvement in Schottky diode p-n junction, MESFET, MOSFET, HBT, and LED devices. >

Critical evaluation of the status of the areas for future research regarding the wide band gap semiconductors diamond, gallium nitride and silicon carbide

Abstract The extreme thermal and electronic properties of diamond and of silicon carbide, and the direct band gap of gallium nitride, provide multiplicative combinations of attributes which lead to the highest figures of merit for any semiconductor materials for possible use in high power, high speed, high temperature and high frequency applications. The deposition of monocrystalline diamond, at or below 1 atm total pressure and at a temperature T , has been achieved on diamond substrates; the deposited film has been polycrystalline on all other substrates but the achievement is no less significant. For electronic applications, heteroepitaxy of single-crystal films of diamond, an understanding of mechanisms of nucleation and growth, methods of impurity introduction and activation, and further device development must be achieved. Stoichiometric gallium nitride free of nitrogen vacancies has apparently not been obtained. Thus, knowledge of the defect chemistry of this material, the growth of semiconducting films on foreign substrates, and the development of insulating layers and of their low temperature deposition as well as device fabrication procedures must be achieved. By contrast, all of these problems have already been solved for silicon carbide, including the operation of a MOSFET at 923 K — the highest operating temperature ever reported for a field-effect device. However, considerable research remains to be done regarding the development of large silicon carbide substrates, of ohmic and rectifying contacts, of new types of devices, and of low temperature techniques for the deposition of insulating layers. Fugitive donor and acceptor species in unintentionally doped samples must also be identified and controlled.

6H-silicon carbide devices and applications

Abstract A variety of devices with promising characteristics have recently been demonstrated in 6H-SiC. There are four primary application areas for 6H-SiC devices: (1) optoelectronics, (2) high-temperature electronics, (3) high-power/high- frequency devices, and (4) nonvolatile memories. These applications, and current device results in each area, are discussed below.

Blue LEDs, UV photodiodes and high-temperature rectifiers in 6H–SiC

Abstract Single junction devices in silicon carbide have been developed for use as blue LEDs, UV photodiodes and high- temperature rectifiers. As a light emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. The most widely commercialized device is the blue LED. Over the past two years, the quantum efficiency of the Cree blue LED has increased significantly. The devices emit light with a peak wavelength of 470 nm with a spectral halfwidth of ∼70 nm. The optical power output is typically between 12 and 18 μW for a forward current of 20 mA at 3 V. This represents a power efficiency of ∼0.02–0.03%. In addition to blue emission, the energy bandgap of ∼3.0 eV allows for inherently low dark currents and high quantum efficiencies for ultraviolet photodiode detectors made in 6H-SiC, even at high temperatures. These devices typically exhibit a quantum efficiency of 80–100% and peak response of ∼250–280 nm. These characteristics are maintained to at least 623 K. The dark current density at -1.0 V and 473 K is ∼10-11 A/cm2. This corresponds to an extrapolated room temperature current density of ∼2 × 10-17 A/cm2 at -1.0 V. Rectifiers with blocking voltages as high as ∼1400 V and a forward current rating of 400 mA at ∼3.0 V have been fabricated. For a 710 V rectifier, the reverse bias leakage current density at 200 V is shown to increase from ∼10-9 to ∼10-7 A/cm2 from 300 to 673 K, respectively. The reverse bias breakdown appears to occur via avalanche multiplication processes exhibiting a sharp knee at breakdown. For a ∼1400 V rectifier, the reverse bias leakage current at 1375 V is less than 1 μA at room temperature.

Progress in SiC : from material growth to commercial device development

Silicon carbide technology has made tremendous strides in the last several years, with a variety of encouraging device and circuit demonstrations in addition to volume production of nitride-based blue LEDs being fabricated on SiC substrates. The commercial availability of relatively large, high quality wafers of the 6H and 4H polytypes of SiC for device development has facilitated these exciting breakthroughs in laboratories throughout the world. These have occurred in numerous application areas, including high power devices, short wavelength optoelectronic devices, and high power/high frequency devices. This paper will describe progress made in increasing the quality and size of SiC wafers, advances in SiC epitaxy and some of the resulting device demonstrations and commercialization by Cree Research.

Electrical properties of ion‐implanted p‐n junction diodes in β‐SiC

Mesa structure junction diodes prepared via high‐temperature ion implantation of Al+ (100 keV, 4.8×1014 Al/cm2) in n‐type or N+ (90 and 180 keV, 0.9 and 1.3×1014 N/cm2) in p‐type β‐SiC thin films were electrically characterized as a function of temperature using current‐voltage and capacitance‐voltage measurements. In either case, rectification was observed to the highest measurement temperature of 673 K. Closer examination of the device current‐voltage characteristics yielded diode ideality factors greater than 2. Additionally, the log dependence of these two parameters indicated space‐charge‐limited current in the presence of traps as the dominant conduction mechanism. From the temperature dependence of log‐log plots, trap energies and densities were determined. Two trapping levels were observed: (1) 0.22 eV with a density of 2×1018 cm−3 and (2) 0.55 eV with a density of 2×1016 cm−3. The former is believed to be ionized Al centers (in the case of Al‐implanted sample) and the latter a compensating accept...

Spontaneous and stimulated emission from photopumped GaN grown on SiC

Photoluminescence of GaN layers grown on 6H–SiC substrates was studied in the temperature range 77–900 K. GaN layers were grown by metalorganic chemical vapor deposition. The temperature dependence of the band gap of GaN was measured throughout the entire temperature range. Edge cavity stimulated emission from photopumped GaN layers was observed in the temperature range 77–450 K. The full width at half‐maximum (FWHM) of the stimulated emission peak was ∼3 nm at 300 K and ∼7 nm at 450 K. Multipass stimulated emission with Fabry–Perot modes was detected from GaN. The FWHM of Fabry–Perot modes was ∼0.2 nm (300 K).

Ion implantation in β-SiC: Effect of channeling direction and critical energy for amorphization

Damage in single-crystal ..beta..-SiC(100) as a result of ion bombardment has been studied using Rutherford backscattering/channeling and cross-section transmission electron microscopy. Samples were implanted with Al (130 keV) and Si (87 keV) with doses between 4 and 20 x 10/sup 14/ cm/sup -2/ at liquid nitrogen and room temperatures. Backscattering spectra for He/sup +/ channeling as a function of implantation dose were initially obtained in the (110) direction to determine damage accumulation. However, the backscattered yield along this direction was shown to be enhanced as a result of uniaxial implantation-induced strain along (100). Spectra obtained by channeling along this latter direction were used along with the computer program t-smcapsr-smcapsIm-smcaps to calculate the critical energy for amorphization. The results for amorphization of ..beta..-SiC at liquid nitrogen and room temperature are approx.14.5 eV/atom and approx.22.5 eV/atom, respectively.

Photoluminescence spectroscopy of ion‐implanted 3C‐SiC grown by chemical vapor deposition

Low‐temperature photoluminescence (PL) spectroscopy has been used to characterize as‐grown and ion‐implanted 3C‐SiC films grown by chemical vapor deposition on Si(100) substrates. The D1 and D2 defect PL bands reported previously in ion‐implanted Lely‐grown SiC were also observed in the as‐grown chemical vapor deposited films, and the effects of annealing (1300–1800 °C) on these PL bands as observed in as‐grown films and films implanted with B, Al, or P have been studied. As reported previously for Lely‐grown SiC, the spectral details of the defect PL bands and their annealing characteristics were found to be independent of the particular implanted‐ion species.

Role of localized and extended electronic states in InGaN/GaN quantum wells under high injection, inferred from near-field optical microscopy

We report on spatially resolved optical measurements of high-quality InGaN/GaN multiple quantum wells under conditions of direct high optical injection (>1019 cm−3) using near-field optical microscopy in the collection mode. The spectral dependence of the spatial distribution of the photoluminescence indicates that the range of In-composition fluctuations reaches the 100-nm lateral scale. The spectra are dependent on the carrier injection level and reveal significant state filling effect. We sketch tentative conclusions about the In-cluster size distribution in terms of contributions to the radiative processes that involve localized and extended states, respectively, in the regime of electron–hole (e–h) pair densities at which present diode lasers operate.