Using current-voltage measurements and high-resolution electron microscopy (HREM), we have studied the electrical and structural properties of Ti contacts on an atomically clean n-type GaAs (110) surface. The Ti/n-GaAs diodes are formed at room temperature in ultrahigh vacuum and in situ isochronally (10 min) annealed at temperatures ranging from 200 to 450°C. We find that the Schottky barrier height of the diodes increases by ≈0.10 eV upon annealing at 200°C and remains basically stable for higher-temperature anneals. HREM investigation reveals that Ti reacts with GaAs in its as-deposited state to form an amorphous interlayer ≈1.5 nm thick. After anneals to 450°C, extensive reactions occur at the interface, resulting in the formation of a layered structure Ti/Ga3Ti2/TiAs/GaAs, with TiAs protruding into the GaAs substrate.

Formation and electronic structure of the Mn/GaAs(100) interface grown at room temperature are studied by photoemission. The growth at early stage is identified to be in two-dimensional mode. The chemical reaction and the interface diffusion happened between Mn and GaAs are explored in some details. A ferromagnetic phase of Mn overlayer at early stage is deduced from the change of electron density of states near the Fermi edge.

A photo chemical vapor deposited silicon dioxide - gallium arsenide interface treated by a selenium(Se)-molecular beam is investigated using extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows the presence of Ga2Se3-related compound at the SiO2/GaAs interface, indicating that the Ga2Se3 layer formed by the Se-treatment is preserved after the deposition of the SiO2film. The effective coordination number of the Se atoms is found to depend on the direction of the polarizing vector with respect to the crystal orientation. An attempt is made to interpret this dependence using a simple atomic layer model.

The Schottky barrier heights of Ni(GaxAl1−x)/n-GaAs contacts have been measured by the I-V and C-V techniques. Contacts with x = 0.0, 0.25, 0.5, 0.75, and 1.0 have been prepared, and a wide range of Schottky barrier heights, 0.66 to 0.96 eV, can be achieved by varying the composition of the alloy contacts. After annealing at 400 °C, the barrier heights increase continuously from 0.66 to 0.96 eV as x decreases. The interfacial stability between the Ni(Ga,Al) contacts and GaAs has been examined by SAM. The modulation of the Schottky barrier height and the interface stability are explained by a thermodynamic and kinetic analysis of the GaAs-NiGa-NiAl-AlAs system.

The degradation mechanism of the Schottky contact of Al/Ti/n-GaAs and Al/Pt/Ti/n-GaAs under the heat treatment of 300°C has been investigated. Barrier height of the Al/Ti/n-GaAs Schottky contact degrades drastically after the heat treatment, in which Ti-Al alloy and Ga out-diffusion have been observed. On the other hand, the barrier height of Al/Pt/Ti/n-GaAs contacts is stable under the heat treatment and, Al-Ti alloying as well as Ga out-diffusion in the metals could not be noticed. From these results, it is presumably concluded that the degradation of the Schottky contacts under the heat treatment is closely correlated with the Ga atom out-diffusion from GaAs surface into the metal films after Al-Ti alloy reach to the GaAs surface. The barrier height reduction after the heat treatment can be explained by the formation of the donor type level at the interface due to the Ga vacancy pile-up arose from the Ga out-diffusion. Pt layer was proved to be an effective barrier suppressing the intermetallic alloying and preventing out-diffusion of Ga.

The growth sequence of Al, Ge, and Ni metals was shown to dramatically affect the amount of heat treatment time required to convert the electrical properties from Schottky to ohmic behavior. Differences in the heat treatment times required to convert from rectifying to ohmic contact were dependent on the doping concentration of the contact layer and on the heat treatment temperature. Interdiffusion of component elements and phase formation have been studied to determine the origin of these effects. Auger depth profiles and X-ray diffraction have been used to determine the interdiffusion and phase formation resulting from various types of thermal processing. Elemental profiles and identification of phases of Ni-Ga, Ni-As, and Ni-Ga-Ge will be used to explain the origin of ohmic behavior.

Using holography and wet chemical etching, a grating of period 450nm and depth of 15nm was fabricated on a n-type GaAs substrate having a doping of 1016 cm−3. A 30 nm layer of Au was deposited on the substrate forming a Schottky contact. The ohmic back contact is an alloy of Ni, Au and Ge. These devices were optically and electrically characterized.

Optical characterization was done using a polarized 632.8 nm HeNe laser. Reflectivity measurements for complete angular scans with output currents were determined. It was observed that as reflectivity dropped to a minimum, at a specific incident angle, the output current peaked. This was attributed to excitation of surface plasma oscillations in the grating, allowing greater photon absorption in the depletion region. This was observed only when the incident electric field was p-polarized and normal to the orientation of the grating, thus satisfying the surface plasma resonance conditions.

Under the above conditions, it was observed that in a grating coupled photodetector a higher quantum efficiency can be achieved.

A thermally stable Pd/Ge/Ti/Pt/ ohmic contact with low specific contact resistance was formed on both n and p+-GaAs. The lowest specific contact resistances were 4.7×10−7 and 6.4×10−7 Ω.cm2 for the n and p+-GaAs, respectively, when the n-GaAs was doped with Si to 2×1018cm−3, and the p+-GaAs was doped with carbon to 5×1019 cm−3. Interfacial reactions and element diffusions of the contacts were investigated by using transmission electron microscopy, Auger electron spectrometry with depth profiles. All the contacts were thermally stable at 300 °C for 20 hours, and it appeared that the p-contacts were more stable than the n-contacts.

The formation of reliable high barrier height Schottky contacts to n-InP is essential for useful device fabrication. Fermi-level pinning traditionally has restricted the application of InP due to large reverse leakage current. Recently, we have proposed the enhancement of Schottky barrier heights (up to 0.98 eV) by deposition with the substrate cooled to low temperature (LT=77K) rather than at room temperature (RT=300K). Studies of the resistance of thin metal films during deposition reveals significant differences in metal nucleation for RT and LT diodes. For the long term stability study, a reverse bias of 2.0V was applied to both RT and LT diodes for more than 1500 hours. Then a constant forward current of 20 mA/cm2 was applied to the diode. The reverse current and forward voltage were recorded as a function of the testing time. After each step the saturation current density (Jo), barrier height (øB), and ideality factor (n) were measured using the current-voltage (I-V) technique. For a LT Au/n-InP diode, the Jo, øB, and n factor were found to be 3.4 × 10−11 A/cm2, 0.98 eV, and 1.31 before testing, and 4.8 × 10−10 A/cm2, 0.92 eV, and 1.31 after testing. The reverse leakage current was nearly constant during the testing. The forward voltage showed a little drop with time. The ultra-high øB and good stability of the LT diodes will be discussed in terms of the interface modification.

A substantial research effort has been devoted to the growth of metals on semiconductors [1], motivated in part by the necessity of electrical contacts and interconnects in semiconducting devices and by the possibility of new physical phenomena and devices derived from the combination of electronic properties of the two materials. Semimetals provide an alternative for applications involving electrical contact, for which their unique transport, optical, and nonlinear properties make them attractive in hybrid devices.

To study the formation of ohmic contacts, several metals have been deposited on p-types ZnTe and ZnSe epitaxial layers. The metals were deposited on the layers either by simple evaporation or by electroplating. The current-voltage characteristics associated with each metal contact were measured. The preliminary results of these measurements indicate that electroplating is a better technique for making ohmic contact to these layers.

Growth characteristics and device applications of heteroepitaxial insulator/semiconductor structures are reviewed. Discussions are made on both fluoride insulators such as CaF2, SrF2, BaF2, LaF3, CeF3, etc. and oxide insulators such as MgOAl2O3, CeO2, ZrO2, (Ba,Sr)O, SrTiO3, etc. First, the growth methods and typical results on the crystalline quality of the films are mainly discussed. In some cases, growth characteristics of semiconductor overlayers on the insulator / semiconductor structures are also discussed. Finally, applications of these structures to future electron devices are reviewed.

Epitaxial thin films of BaF2 were deposited for the first time onto (100) InP at a substrate temperature of around 450°C to 480°C by RF magnetron sputtering. The structural properties of the BaF2 film were a strong function of the substrate temperature during film deposition. X-ray diffraction analysis revealed a pure c-axis orientation perpendicular to the substrate surface. Scanning electron microscopy surface scan indicated a highly textured film with grid growth morphology. Ellipsometry measurement on the films gave a refractive index in the range of 1.4 to 1.6. The capacitance vs voltage analysis on a capacitor with a structure of Au/BaF3/InP demonstrated a dielectric constant of around 7.3 for the BaF2.

We report on growth, doping, and characterization studies of GaN films produced by the Electron Cyclotron Resonance microwave plasma assisted Molecular Beam Epitaxy. The films were grown heteroepitaxially on sapphire (0001), whose surface was converted into atomically smooth AIN by plasma nitridation. The GaN films were grown in two temperature steps, a process found to promote the layer-by-layer growth mode. ECR plasma conditions to grow either n-type autodoped or semi-insulating GaN film were identified. The structure and microstructure as well as the electrical properties of these two classes of films are discussed. A systematic dependence between electron mobility and net carrier concentration was found, which predicts that the mobility of GaN with a net carrier concentration of 1014cm−3 is about 104cm2 /V.s. The insulating films were intentionally doped either p-type or n-type by incorporation of Mg or Si during film growth. Hole or electron concentrations at 300K between 1018-1019cm−3 have been obtained without requiring any post-growth treatment.

High electron mobility autodoped GaN films were produced by the ECR assisted MBE method. The net electron concentration was varied systematically from 2×1019 to 2×1017cm−3 by controlling the active nitrogen overpressure. Correspondingly, the electron mobility increased from 20 to 210 cm2V−1sec−1. The line through the experimental data also predicts the electron mobilities of GaN films produced by the CVD methods.

In this paper we report the fabrication and characterization of a metal insulator semiconductor field effect transistor (MISFET) based on single crystal GaN-AlxGa1−xN heterostructures. The device structure layers were deposited over sapphire substrate using low pressure metalorganic chemical vapor deposition. We discuss the fabrication and characterization of MISFET devices using single crystal GaN as the insulator layer. These were fabricated on isolated mesas using TiAu for the source and drain ohmic contacts and silver for the gate Schottky. For devices with a gate length of 4 μm (channel opening i.e. source to drain separation of 10 μm), a transconductance of 20 mS/mm was obtained at -1 volt gate bias. Complete pinchoff was observed for a gate potential of -15 volts. Device performance is compared to that for a GaN MESFET of identical dimensions.

Due to its direct bandgap tunable from 3.4 to 6.2 eV AlxGa1−xN is an important semiconductor for devices in the ultraviolet and visible parts of the spectrum. The large bandgap, potential of heterojunction formation and the insulating nature of AlN make AlxGa1−xN an ideal material system for high performance metal semiconductor field effect transistor (MESFET) devices requiring high operation temperatures. Availability of the insulator (single crystal AlN or GaN) also makes possible the fabrication of metal insulator field effect transistor (MISFET) devices which has been an elusive goal for the GaAs based III-V materials technology.

High quality single crystal GaN films have been deposited on sapphire and several other semiconductor substrates using metalorganic chemical vapor deposition (MOCVD)1,2, molecular beam epitaxy (MBE)3 and vapor phase epitaxy (VPE)4. Recently we have reported on quantum confinement5, room temperature stimulated emission6, and 2-dimensional electron gas in GaN-AlxGa1−xN heterostructures7,8. We have also deposited single crystal insulating GaN and A1N over sapphire using atomic layer epitaxy9,10 and fabricated high responsivity photoconductors11. We now report on the fabrication and characterization of FET devices using single crystal GaN-AlxGa1−xN heterostructures. This forms the basis of high temperature transistor devices based on the AlxGa1−xN material system.

A theory of electronic structures of NGaN×NAlGaN GaN/Alx Ga1−xN wurtzite semiconductor superlattices (grown in the direction of the c-axis) is developed and used to predict the superlattices' band structures, energy gaps, and the “deep” energy levels of substitutional s- and p-bonded defects in them. In addition, the valence band offset of GaN with respect to AlN, the one adjustable parameter of the theory, is determined to be about 0.4 times the total fundamental band-gap difference, by fitting the optical data for the superlattices' fundamental band gaps as a function of the layer thicknesses NGaN and NAlN, with the valence band edge of AlN being at lower energy.

Electronic band structures, equilibrium lattice constants and structural parameters, cohesive energies, and bulk moduli calculated by means of the linear-muffin-tin orbital method are presented for BeSiN2, MgSiN2 and MgSiP2 chalcopyrites. The relationships of these compounds to the “parent” III-V compounds are clarified.

Heterostructures of SiC and AlN in either sequence, AlN on SiC or SiC on AlN, were grown on Si, Al2O3, and 6H-SiC substrates by (metalorganic) chemical vapor deposition (CVD). On Si substrates, a SiC layer was first grown by a two-step technique and an AlN layer was deposited subsequently. On other substrates, an AlN layer was first grown, followed by SiC deposition. Multi-layered structures (SiC/AlN/SiC) were also produced to demonstrate the ability of heteroepitaxy of SiC and AlN on each other.

AlN grown on 3C-SiC were highly oriented polycrystalline films. AlN films on 6H-SiC, SiC films on A1N/Al2O3, and SiC films on AlN/6H-SiC were single crystal. In the latter two cases, the SiC films were in hexagonal structure. These SiC films were smooth and specular in appearance and showed n-type conductivity.

We report on the low temperature growth of heteropolytype junctions of 3C-SiC on 6H-SiC by low pressure chemical vapor deposition. In this work we have observed the epitaxial layers to be single crystal below a critical thickness limit which depends on growth temperature. Films thicker than this limit are polycrystalline. At 1150 C we have found the critical thickness to be approximately 2500 angstroms.