Basal plane sapphire is a common substrate for the heteroepitaxy of GaN. This presents a challenge for fabrication of cleaved facet GaN lasers because the natural cleavage planes in (0001) α-A12O3 are not perpendicular to the wafer surface. This paper describes a method for achieving perpendicular cleaved facets through wafer fusion that can potentially be used to fabricate GaN based in-plane lasers. We demonstrate successful fusion of GaN to InP without voids or oxide at the interface and fabricate optically flat cleaved GaN facets that are parallel to the crystallographic planes of the host InP. I-V measurements have been performed across the n-N fused interface. These results show that the fused interface exhibits a barrier for electrons passing from the InP to the GaN and ohmic conduction of electrons moving in the opposite direction.

Subband structures and optical gains of the strained wurtzite GaN/AlGaN quantum well lasers are theoretically investigated on the basis of k.p theory. First-principles calculations are used for deriving the unknown physical parameters, such as deformation potentials. Neither compressive nor tensile biaxial strains are so effective on the reduction of the threshold carrier density. It is also found that the uniaxial strain in the c-plane is one of the preferable approaches for the efficient improvement of the laser performance.

The reliability of devices fabricated in GaN and related alloys, especially under high current densities as would be found in lasers, has yet to be fully characterized. Our previous work [1] investigated the degradation of GaN-based blue light emitting diodes (LEDs) under high pulsed current stress. This work indicated a possible correlation between the high crystal defect density and failures caused by metal migration along these defect tubes. To assess the impact of this data on devices under more normal conditions, several LEDs from both older and more recent production lots were placed in a controlled temperature and current environment for several thousand hours. The test started with a constant 20 mA current for the first 1000 hours and continued for another 1650 hours at various currents up to 70 mA, all at a temperature of 23 °C. During this test, one of the older generation LED's output degraded by more than 50%. Subsequent failure analysis showed that this was caused by a crack which isolated part of the active region from the p-contact. The remaining LEDs were returned to life testing where the temperature was subsequently increased by 5 °C after each 500 hours of testing. The output from one of the newer LEDs dreiven at 70 mA degraded to 55% of its original value after 3600 hours and a second newer LED degraded by a similar amount after 4400 hours. The first failure, LED #16, did not exhibit a significant change in its I-V characteristics indicating that a change in the package transparency was a likely cause for the observed degradation. The second failure, LED #17, did show a noticeable change in its I-V characteristics. This device was subsequently returned to life testing where the degradation process will be monitored for further changes.

We have examined the effect of growth conditions on photoluminescence (PL) characteristics of chloride VPE-grown GaN films. Undoped GaN films are grown on sapphire by a newly developed chloride VPE system which utilizes GaCl3 and NH3 as source materials.

We find that the spectra depend strongly on the growth temperatures and the corresponding surface morphology. Peaks from excitons and donor-acceptor pairs (D-A pair) recombination are observed for the films with terrace-like flat surfaces grown at between 950°C and 1000°C. A peak due to exciton bound to neutral donors is observed for a growth temperature of 975°C where the acceptor-related peaks are not seen. Decreasing the growth temperature below 950°C causes rough surfaces due to three-dimensional growth, whereas increasing the growth temperature above 1000°C causes cracks or partial pealing off of the film. The films with rough surfaces or crystal failures show broad emission from deep acceptor levels. As a result, residual acceptors are eliminated in the very narrow range of the growth temperature around 975°C. It is also noted that an increase of the V/III ratio during the growth makes the line width of the band-edge peak narrower. The PL results show that a growth temperature around 975°C and high V/III ratio are essential to obtain better crystal quality and reduced concentration of residual acceptors.

GaN films with good crystalline quality are grown on sapphire by atmospheric pressure vapor phase epitaxy using gallium tri-chloride (GaCl3) and ammonia (NH3). Epitaxial growth is carried out over temperature and V/III-ratio ranges of 800–1000°C and 100–1000, respectively. Typical growth rate obtained is in the range of 5–20 μm/hr. The films grown below 925°C typically show three dimensional (island) growth, while above that temperature, continuous films are obtained. Films grown at 975°C with a V/III ratio > 300 exhibit a smooth surface. XRD analysis shows that the films are single crystal with hexagonal polytype. Strong band-edge photoluminescence is observed with a FWHM of 60 meV at room temperature and 25 meV at 77K. The results indicate that this simple growth technique is effective for growing high quality bulk GaN, which can be used as a substrate for subsequent epitaxy. In order to further improve the surface morphology, a preliminary experiment on GaN growth on a thin GaN buffer layer prepared by gas source MBE is also presented.

Over an order of magnitude reduction in dark current was observed for gas-source molecular beam epitaxially (GSMBE) grown, lattice-matched n- and p-type InGaAs/InP quantum-well infrared photodetectors (QWIPs). Peak spectral response at 8.93 and 4.55 μm for n- and p-type QWIPs, respectively, open the possibility of dual-band monolithic integration under identical GSMBE growth conditions.

Ion implantation has been an enabling technology for the realization of many high performance electronic devices in III-V semiconductor materials. We report on advances in ion implantation processing technology for application to GaAs JFETs, AlGaAs/GaAs HFETs, and InGaP or InA1P-barrier HFETs. In particular, the GaAs JFET has required the development of shallow p-type implants using Zn or Cd with junction depths down to 35 nm after the activation anneal. Implant activation and ionization issues for AlGaAs will be reported along with those for InGaP and InAlP. A comprehensive treatment of Si-implant doping of AlGaAs is given based on the donor ionization energies and conduction band density-of-states dependence on Al-composition. Si and Si+P implants in InGaP are shown to achieve higher electron concentrations than for similar implants in AlGaAs due to the absence of the deep donor (DX) level. An optimized P co-implantation scheme in InGaP is shown to increase the implanted donor saturation level by 65%.

The influence of non-stoichiometry on the solid-phase epitaxial growth of amorphized GaAs has been studied with in-situ Transmission Electron Microscopy (TEM). Ion-implantation has been used to produce microscopic non-stoichiometry via Ga and As implants and macroscopic non-stoichiometry via Ga or As implants. It has been demonstrated that amorphous GaAs recrystallizes into a thin single-crystal layer and a thick heavily twinned layer. Video images of the recrystallization process have been quantified for the first time to study the velocity of the crystalline/amorphous (c/a)-interface as a function of depth and ion species. Regrowth rates of the single crystal and twinned layers as functions of non-stoichiometry have been calculated. The phase transformation is rapid in Ga-rich material. In-situ TEM results are consistent with conventional in-situ Time Resolved Reflectivity, ex-situ Rutherford Backscattering Spectroscopy and Channelling measurements and ex-situ TEM.

Development of a complementary heterostructure field effect transistor (CHFET) technology for low-power, mixed-mode digital-microwave applications is presented. An earlier digital CHFET technology with independently optimizable transistors which operated with 319 ps loaded gate delays at 8.9 fJ is reviewed. Then work demonstrating the applicability of the digital nJFET device as a low-power microwave transistor in a hybrid microwave amplifier without any modification to the digital process is presented. A narrow band amplifier with a 0.7 × 100 μm nJFET as the active element was designed, constructed, and tested. At 1 mW operating power, the amplifier showed 9.7 dB of gain at 2.15 GHz and a minimum noise figure of 2.5 dB. In addition, next generation CHFET transistors with sub 0.5 μm gate lengths were developed. Cutoff frequencies, ft of 49 GHz and 11.5 GHz were achieved for n- and p-channel FETs with 0.3 and 0.4 μm gates, respectively. These FETs will enable both digital and microwave circuits with enhanced performance.

Changes in sheet resistance of n- and p-type InGaP exposed to Electron Cyclotron Resonance Ar plasmas have been used to measure the introduction of ion-induced damage. P-type material is much more resistant to change in its conductivity than n-type InGaP, indicating that electron traps are the predominant entity produced by the ion bombardment. For short (˜1 min.) plasma exposures the ion current is more important than ion energy in producing resistance changes. Annealing of damage in both conductivity types occurs with an activation energy of ˜3.4±0.5eV. p+A1GaAs is found to be much more susceptible than n+AlGaAs to the introduction of electrically active deep levels during exposure to Electron Cyclotron Resonance Ar plasmas. In both AlGaAs materials the resistivity of thin (˜0.5μm) epitaxial layers increases rapidly with both plasma exposure time and the ion energy, while the ion density in the Ar discharge has a much greater influence on p+AlGaAs than n-type material. These results suggest that the energetic ion bombardment introduces deep hole traps more readily than deep electron traps in AlGaAs and that pnp transistor structures will be more susceptible to plasma damage than comparable npn structures.

Electron cyclotron resonance (ECR) etching of GaP, GaAs, InP, and InGaAs are reported as a function of percent chlorine-containing gas for Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2 plasma chemistries. GaAs and GaP etch rates were faster than InP and InGaAs, independent of plasma chemistry due to the low volatility of the InClx, etch products. GaAs and GaP etch rates increased as %Cl2 was increased for Cl2/Ar and Cl2/N2 plasmas. The GaAs and GaP etch rates were much slower in BCl3-based plasmas due to lower concentrations of reactive Cl, however enhanced etch rates were observed in BCl3/N2 at 75% BCl3. Smooth etched surfaces were obtained over a wide range of plasma chemistries.

Etching of β-SiC with electron cyclotron resonance (ECR) system was investigated. Anisotropic and smooth etching of SiC was demonstrated with SF6/O2 based discharges. The root-mean-square roughness increases from 35 nm to 56 nm for as deposit and etched sample, respectively. The addition of small amount oxygen enhanced the etch rate of SiC slightly, but further increase of oxygen content reduced the etch rate which resulted from dilution of F ion and free radical densities. NF3/O2 based discharges also showed same trends and produced anisotropicly etching. However, the smoothness is not as good as SF6/O2 based discharges.

Depositing Pd or Au on n-InP at cryogenic substrate temperatures has previously been found to significantly increase the barrier height of the resulting Schottky diode. Cross-sectional transmission electron microscopy (XTEM) has been performed on Pd/InP and Au/InP interfaces formed at room temperature (RT) and low temperature (LT) to determine the differences responsible for the change in barrier height. In the Pd case, a solid state amorphization which occurs at the interface upon RT metal deposition is nearly eliminated in as-deposited LT Pd/InP diodes. In the Au case, RT deposition results in the initial monolayers of Au entering the InP lattice, while no such effect was observed in the LT Au/InP diodes. It is clear that the LT deposition dramatically reduces the interaction between the metal and substrate, resulting in a greater barrier height. Enhanced barrier height Schottky diodes are crucial to the development of optical and electronic devices on InP. Preliminary results will be discussed on metalsemiconductor- metal (MSM) photodetectors and metal-semiconductor field-effect-transistors (MESFET's) fabricated using the LT process.

The deep-level defects in 10 MeV electron irradiated undoped semi-insulating (SI) LEC GaAs were investigated. The results show that the density of EL2 (Ec-0.83eV) and EL12 (Ec-0.69eV) defects increases and the density of EL6 (Ec-0.39eV) and EL3 (Ec-0.58eV) defects decreases in irradiated SI-GaAs at higher fluence levels. At lower fluences, we observe decrease in density of EL2 and EL12 defects, however, the density of the EL6 and EL3 defects is increased. It could be related mainly to the dissociation of the EL2 and EL12 defects. The influence of 10 MeV electrons irradiation on the resistivity will also be discussed.

We present annealing behavior for EL2 and EL6 groups as dominant deep levels in semiinsulating GaAs using Photo Induced Transient Spectroscopy (PITS) measurement. During rapid thermal annealing, a relation has been identified between EL2 group at 0.79 and 0.82 eV and EL6 group at 0.24, 0.27 and 0.82 eV below the conduction band. It is found that they may be close in structure, and belong to the EL2 and EL6 groups, respectively. In rapidly annealed samples, the quantity of all defects in the EL2 group increases, while that in the EL6 group decreases. However, by furnace annealing at 950°C for 5 hours, some of the defects in the EL2 group break up, and the quantity of all defects in the EL6 group increases. It is suggested that the EL2 group and EL6 group are related in their microscopy structures. We then discuss a relation between the two groups and their origins.

The built-in electric fields in a MBE grown δ-doped GaAs homojunction have been investigated by the techniques of photoreflectance and phase suppression. Two Franz-Keldysh oscillation features originating from two different fields in the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase of the lock-in amplifier, one of the features can be suppressed, thus enabling us to determine the electric fields from two different regions. We have demonstrated that only two PR spectra, in-phase and outphase components, are needed to find the phase angle which suppresses one of the features. The electric field in the top layer is 3.5 ± 0.2 × 105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2 ± 0.1 × 104 V/cm, which suggests the existence of interface states at the buffer/substrate interface.

technique, on both semi-insulating and semi-conducting CraAs substrates with (100) orientation, offset by 2° towards (110) direction. Systematic variation of As/Ga was performed to gain an understanding of growth process, type of formation and other related physical properties. The films were characterized by using the variety of techniques, such as SEM, EDAX, HRTEM, XRD, and PL. Optical and electrical properties of undoped CyaAs epilayers are presented with reference to the growth conditions and AsH3/TMGa ratio. Photoluminescence measurements of GaAs epilayers were recorded at 4.2K and shows the emission of free exciton and confirmed their high purity. The dominant residual impurities in GaAs are presented by using PL. Finally, electrochemical depth profiling exhibited almost homogeneous background carrier distribution and excellent abruptness between the thin GaAs epilayer and substrate.

We report a new semiconducting Ge-Si-Fe alloy thin film grown on Si(100) by reactive deposition epitaxy(RDE) using high vacuum evaporation technique. AES and XRD results show that the new alloy can be regarded as a distorted β-FeSi2 with the Ge participation. The direct band gap of the Ge-Si-Fe alloy was determined to be 0.83eV by optical transmission measurement, which means a red shift of band gap compared with that of β-FeSi2 (Eg=0.87eV).

We report the effects of growth conditions on the strain and crystalline quality of lowtemperature (LT) grown GaP films by gas-source molecular beam epitaxy. At temperatures below 160 °C, poly-crystalline GaP films are always obtained, regardless of the PH3 low rate used, while at temperatures above 160 °C, the material quality is affected by the PH3 flow rate. Contrary to compressively strained LT GaAs, high-resolution X-ray rocking curve measurement indicates a tensile strain of the LT GaP films, which is considered to be due to PGa antisite defects. The strain is found to be affected by the PH3 flow rate, the growth temperature, and post-growth annealing. Contrary to LT GaAs, no P precipitates are observed in cross-sectional transmission electron microscopy.

Interest in room-temperature operable quantum effect devices has created a need for simple and inexpensive nanofabrication techniques. By applying a bias to a conductive AFM tip, we have succeeded in fabricating narrow (˜30 nm) oxide lines on a variety of metal and III-V semiconductor substrates. The effects of different drawing parameters such as tip bias, translation speed, ambient atmosphere, and substrate doping on line quality were explored.