Electron cyclotron resonance (ECR) plasma etching of single crystal 6H-SiC has been investigated using a CF4/O2 gas mixture and compared to conventional reactive ion etching (RIE) in a radio frequency (13.56 MHz) reactor. The use of ECR results in higher etch rates, lower levels of bias and smoother etched surfaces than rf-RIE. ECR etch rates exceeding 100 nm/min have been obtained at a substrate bias of-100 V. Etch rate and surface morphology have been studied as a function of pressure, bias and power. Auger electron spectroscopy shows that ECR etching leaves no residues unlike rf-RIE which leaves residues containing Al, F, O and C. The current-voltage and capacitance-voltage measurements of Schottky diodes show that there is far less damage induced by ECR etching compared to rf-RIE.

ABSTRACT:In SiC junctions, it is usual to find the ideality factor n=2 (or slightly higher) in 6H-SiC and n>2 and temperature dependent for 3C-SiC. However, the recombination current yields an ideality factor no higher than 2. This value can be slightly increased by considering the Poole-Frenkel effect (PFE), so that the 6H-SiC junction characteristics can be properly fitted. On the other hand, 3C-SiC junction characteristics, which are quite different from the ideal ones, cannot be satisfactorily explained on the basis of this model and the multitunnel capture-emission mechanism is proposed as the responsible for this behavior.

We report the fabrication and the characterization of Metal Oxide Semiconductor (MOS) structure fabricated on thermally oxidized 3C-SiC grown by reactive magnetron sputtering. The structure and the composition of the SiO2 layer was studied by cross-sectional transmission electron microscopy (XTEM) Auger electron spectroscopy (AES). Homogeneous stoichiometric SiO2 layers formed with a well-defined interface to the faceted SiC(lll) top surface. Electrical properties of the MOS capacitor have been analyzed by employing the capacitance and conductance techniques. C-V curves shows the accumulation, depletion and deep depletion phases. The capacitance in the inversion regime is not saturated, as usually observed for wide-bandgap materials. The unintentional doping concentration determined from the 1/C2 curve was found to be as low as 2.8 × 1015 cm-3. The density of positive charges in the grown oxide and the interface states have been extracted by using high-frequency C-V and conductance techniques. The interface state density has been found to be in the order of 1011cm2-eV-1.

Availability of optoelectronic components operating in the U V-Visible part of the spectrum opens several exciting and important system applications. Solid state ultraviolet and blue-green lasers can increase the optical data storage density of CDROM/WORM and magneto-optical disks by a factor of four. They are also ideally suited for environmental pollutant identification and monitoring. On the other hand, solid state ultraviolet detectors that do not respond to visible or IR radiation are highly desirable for various commercial systems. These include medical imaging, industrial boiler systems, fire/flame safeguard systems around oil and gas installations and several military applications. A key requirement for these ultraviolet laser and sensor devices is the availability of a semiconductor material system with high quality controlled doping and fabrication technology.

AlxGa1−xN and InxGa1−xN for which the direct bandgap can be tailored from the visible to the deep UV is such a material system. Ours and several other research groups (nationally and internationally) have been developing AlxGa1−xN materials and processing technologies over the past several years. Recently, by employing innovative approaches, significant advances have been made in heteroepitaxy of AlxGa1−xN on sapphire substrates. Also, controlled n and p-type doping has been achieved. Several high performance devices that form the basis of exciting future research have been demonstrated. These include high responsivity visible blind ultraviolet sensors, basic transistor structures and high power blue light emitting diodes. These pave the way for future research leading to exciting products such as blue-green lasers and UV-imaging arrays. The demonstrated transistor structures are foundation for building AlxGa1−xN -GaN based high power, high frequency and high temperature electronic components. In this paper, we will summarize some of our recent work and reflect on the potential and the issues in AlxGa1−xN-InxGa1−xN based device development.

High-brightness InGaN/AlGaN double-heterostructure (DH) blue-light-emitting diodes (LEDs) with a luminous intensity of 1.2 cd were fabricated successfully for the first time. As an active layer, a Zn-doped InGaN layer was used. The peak wavelength and the full width at half-maximum of the electroluminescence were 450 nm and 70 nm, respectively. The forward voltage was as low as 3.6V at 20 mA.

Dry patterning of GaN, InN, AlN and InGaN grown by MOMBE on GaP, Al2 O3 or GaAs substrates was performed with 100–500 eV Ar+ ions at beam angles of incidence ranging from 0–75° from the normal, or with ECR discharges of BCl3/Ar, CH4/H2 or Cl2/H2. The mill rates normalized to the Ar+ beam current were typically a factor of 2 lower than for GaAs and InP (i.e. maximum values of 300–500 Å·min-1·mA-1·cm-2 at 400eV Ar+ beam energy and 60° angle with respect to the beam normal). The surface morphology of the ion milled nitrides was smooth even at 500 eV Ar+ energy, with no evidence for preferential sputtering of N as determined by AES. The ECR dry etch rates were fastest with elevated temperature Cl2/H2discharges, although both of the other chemistries investigated provide smooth, anisotropie pattern transfer. Since the ion mill rates are slow for single-crystal nitrides and less than the mill rates of common masking materials (SiO2, SiNx, photoresist) it appears this technique is useful only for shallow-mesa applications, and that dry etching methods involving an additional chemical component or ion implantation isolation are more practical alternatives for device patterning.

Diamond films produced by microwave plasma enhanced chemical vapor deposition (CVD) technique and used to fabricate radiation detectors have been characterized. The polycrystalline diamond films have a measured resistivity of 1012 Ω.cm and a carrier lifetime of about 530 ps. The carrier mobility - lifetime product depends on the density of photogenerated carriers. The carrier mobility decreases from 160 to 13 cm2/V.s for a carrier density increase from 2 × 1011 cm-3 to 3.7 × 1013 cm-3. The detector response to laser pulses (λ= 355, 532 and 1064 nm), X-ray flux (2.5 – 16 keV) and alpha particles (241Am, 5.49 MeV) has been investigated. The response speed of the detector is in the 100 ps range. X-ray photon flux measurements and alpha particle counting capabilities of the CVD diamond detectors are demonstrated.

We are reporting the first quantitative photoresponse characteristics of boron doped hot-filament CVD (HFCVD) diamond based Schottky diodes using semi-transparent aluminum contacts in the spectral range of 300–1050 nm. Quantum efficiencies, obtained without correction for surface reflection in the visible and near UV region, were between 5 % and 10% when the diodes were unbiased. Effect of reverse bias on the photoresponse was investigated at selected photon energies. Reverse biased diodes exhibit increasing photoresponse and ultimately saturation. Quantum efficiency as high as 30% was also obtained at 500 nm, when a reverse bias of over I volt was applied. The photoresponse mechanism of CVD diamond Schottky diodes is also discussed. A Schottky barrier height of 1.15 ± 0.02 eV for Al-HFCVD diamond contacts was determined using the d.c. photoelectric method.

The evolution of the damage in the near surface region of single crystalline 6H-SiC generated by 200 keV Ge+ ion implantation at room temperature (RT) was investigated by Rutherford backscattering spectroscopy/chanelling (RBS/C). The threshold dose for amorphization was found to be about 3 · 1014 cm-2, Amorphous surface layers produced with Ge+ ion doses above the threshold were partly annealed by 300 keV Si+ ion beam induced epitaxial crystallization (IBIEC) at a relatively low temperature of 480°C For comparison, temperatures of at least 1450°C are necessary to recrystallize amorphous SiC layers without assisting ion irradiation. The structure and quality of both the amorphous and recrystallized layers were characterized by cross-section transmission electron microscopy (XTEM). Density changes of SiC due to amorphization were measured by step height measurements.

Oxygen is a commonly used etchant of carbon materials, including diamond. In this work, we examine the effects of oxygen ion bombardment to diamond surfaces, as might be encountered in a reactive ion etching (RIE) process. Surfaces were characterized using Electron Energy Loss Spectroscopy (EELS) and Auger Electron Spectroscopy (AES). EELS was used to determine the presence of non-diamond carbon at the surface which may form due to ion damage. AES was used to determine the presence of oxygen on the diamond surface from oxygen ion bombardment. The effect of ambient molecular oxygen present during inert ion bombardment is also addressed. EELS was also used to determine the state of diamond surfaces that were bombarded with hydrogen ions, as might be used in the removal of adsorbed oxygen.

Monocrystalline 6H silicon carbide samples (n-type and p-type) with both carbon face and silicon face have been used to investigate gate oxide quality. The oxides were thermally grown in a dry oxygen ambient at 1523 K with or without the addition of TCA (Trichloroethane), or in wet pyrogenic steam at 1473 K. POCI3 doped polysilicon gates were used for electrical characterisation by capacitance-voltage measurements and breakdown field measurements. Large flatband voltage shifts indicate fixed oxide charges up to 1013 cm-2. The incorporation of aluminum in the oxides was monitored using SIMS (Secondary Ion Mass Spectrometry). Surprisingly high signals were interpreted as evidence of an aluminum-Oxygen compound having been formed (ie Al2O3).

Schottky diodes on Silicon Carbide (SiC) are of interest for many applications because of the relatively simple fabrication process. In this work we have fabricated Schottky diodes by evaporation of Ti on 6H-SiC and measured their electrical and optical properties. Most of the diodes show good rectifying behaviour with low reverse current and an ideality factor below 1.20. The photoresponse of the diodes has been measured in the range 200 – 400 nm. The peak sensitivity was found to be at 270 nm.

Gallium nitride has generated much interest due to its ability to emit light in the blue to UV range [1]. We have investigated the ohmic contact properties of various metals evaporated onto highly auto-doped n-type GaN thin films which were grown on basal sapphire substrates by ion-assisted molecular beam epitaxy (IAMBE). Electrical measurements of transmission line structures with the metals In, InSn and AuGeNi revealed a wide range of contact resistivity (10∼2 to 10-6 Ω-cm2) which changed with annealing.

Materials and electrical evaluation were performed to determine the characteristics of ohmic contacts to 6H-SiC. Both elemental metal (Co) and suicides (CoSi and CoSi2) were studied following heat treatments at 500 °C and 900 °C for 5 hours and 2 hours, respectively. Materials analysis by Rutherford Backscattering Spectrometry (RBS) and X-ray Diffraction (XRD) monitored the temperature stability of the contacts after the annealings. Current density-voltage measurements at elevated temperatures established the specific contact resistance pc.

Three types of electrical contacts on natural type lib single crystal diamonds have been studied by current-voltage (IV) and capacitance-voltage (CV) measurements. Vertical structures were fabricated with the metal-diamond (MS), metal-undoped diamond-doped diamond (MiS), or metal-SiO2-doped diamond (MOS) contacts and ohmic contacts on the opposite face of the diamond. The MS contact was rectifying and both the MiS and MOS were blocking contacts. While very high leakage currents were measured on the MiS structure in forward bias (MO6times the reverse bias), an accumulation region was observed in the MiS CV data. The uncompensated acceptor concentration values calculated from the CV data were in good agreement for different structures fabricated on the same samples and with the secondary ion mass spectroscopy (SIMS) measurements of the bulk boron concentration. Extreme stretch out was observed in the CV of the MiS and MOS due to interface traps. The density of interface traps was estimated to be in the 1012 cm-2 eV-1 range for these structures.

Copper films were grown on a single crystal diamond substrate using an iron seed layer. The effect of the crystalline structure of the iron seed on the Cu films was studied with extended x-ray absorption fine structure (EXAFS) and scanning electron microscopy (SEM). The EXAFS study shows that the 10 Å Fe seed layer is in an fee structure, and has collapsed into a bec structure by the time 20 Å of Fe has been deposited. In the SEM pictures it is observed that subsequent layers of Cu grow as continuous films for thin fcc-Fe seeds, and grow in an island mode for the thick, bcc-Fe seeds.

The thermally induced solid-phase reaction of 135 nm thick sputter-deposited W films with polycrystalline CVD-grown diamond substrates is investigated. The samples are annealed in vacuum (5×10/-7 torr) at temperatures between 700 °C and 1100 °C for 1 hour and examined by 2 MeV 4He++ backscattering spectrometry, x-ray diffraction, and scanning electron microscopy.

The as-deposited W films contain roughly 5 at.% oxygen. After annealing the samples at 800 °C this oxygen concentration falls below the detection limit of less than 1 %. Incipient W2C phase formation occurs during annealing at 900 °C. The final state, the WC phase, is reached after annealing at 1100 °C.

It is becoming increasingly apparent that future progress in diamond chemical vapor deposition depends on deeper understanding of the underlying mechanism of surface processes. Substantial efforts toward this goal have led to several conclusions on which consensus is beginning to emerge. Among them are the mediating role of hydrogen atoms, generic features of the growth kinetics, thermodynamic stability of reconstructed (100) surfaces, and the insertion reaction of methyl into (100)-(2×l) dimers. Despite these efforts, an overall picture of diamond growth in terms of elementary processes is still lacking. In this paper, the current state of mechanistic understanding is reviewed, emphasizing common themes, and new results are presented. Among the latter are the effect of reaction reversibility on surface morphology, surface migration, and a new mechanism for diamond growth from acetylene.

Rate, crystallinity and phase purity of vapor-grown diamond deposits are discussed. Emphasis is on microwave plasma CVD of diamond from C/H-, C/H/O-, C/H/F-, C/H/CI- and C/H/N-gas mixtures.

The manufacture of wear-resistant diamond thin films, diamond vacuum window membranes and thick diamond heat spreader plates are used as examples to outline the influence of various deposition parameters on the performance of finished products and to describe the use of ternary gas phase compositional diagrams as tools for minimization of deposition technology and product optimization efforts.

Growth and etch rates for diamond homoepitaxy have been measured in situ using Fizeau interferometry. Experiments were conducted in a hot-filament reactor using hydrogen, methane, and oxygen feed gases at a reactor pressure of 25 torr. The substrate temperature dependence for growth on diamond(lOO) was studied for 0.5% and 1% CH4 and 0–0.44% O2. Apparent activation energies of 17 and 5 kcal/mol were determined for growth from 0.5% and 1% CH4 in hydrogen, over the ranges of 700 – 1000 °C and 800 – 1050 °C, respectively. When a minimal amount of Oxygen was added to the feedstock, the growth-rate behavior was similar for that with pure methane. With greater amounts of added oxygen, growth rates were higher than those without Oxygen at low temperatures, proceeded through a maximum, and then decreased until etching was observed at high temperatures. Similar behavior was observed for growth from 1% CH4 with and without oxygen. We also measured the temperature dependence for etching of homoepitaxial diamond films in hydrogen with 0–0.1% O2, and observed etch rates of 0.01 – 0.1 microns/hr in the range of 950 – 1150 °C. We propose that oxygen facilitates diamond growth at low temperatures by enhancing the removal of both sp2- and sp3-bonded “errors” and/or by increasing the efficiency of carbon incorporation by roughening the diamond surface, and that these etching processes become dominant at high temperatures.