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The boron phosphide (BP) semiconductor has many remarkable features, including high thermal neutron capture cross section of the 10 B isotope, making it attractive for neutron detection applications. Effective and efficient neutron detection require BP to also have high crystal quality with optimum electrical properties. Here, we present the heteroepitaxial growth of high quality BP films on a superior aluminum nitride(0001)/sapphire substrate by chemical vapor deposition. The effect of process variables on crystalline and morphological properties of BP was examined in detail. BP deposited at high temperatures and high reactant flow rate ratios produced films with increased grain size and improved crystalline orientation. Narrower full width at half-maximum values of BP Raman peaks (6.1 cm −1 ) and ω rocking curves (352 arcsec) compared to values in the literature confirm the high crystalline quality of produced films. The films were n-type with the highest electron mobility of 37.8 cm 2 /V·s and lowest carrier concentration of 3.15 × 10 18 cm −3 . Rotational twinning in BP due to degenerate epitaxy caused by 3-fold BP(111) on 6-fold AlN(0001) was confirmed by synchrotron white beam X-ray topography. This preliminary study showed that AlN is an excellent substrate for growing high quality BP epitaxial films with promising potential for further enhancement of BP properties.

In a series of ferroelastic urea inclusion compounds (UICs), in which domain reorientation occurs upon application of an external anisotropic force, introduction of a relaxive impurity that disrupts a specific hydrogen-bonding network transforms a plastic (irreversible) domain-switching process into one that exhibits a striking memory effect and “rubber-like behavior”, a form of pseudoelasticity. As expected for a highly cooperative process, the ferroelastic response to the impurity concentration exhibits a critical threshold. Through synchrotron white-beam X-ray topography (SWBXT) of crystals under stress, videomicroscopy of spontaneous repair during crystal growth, acoustomechanical relaxation of daughter domains, kinetic measurements of spontaneous domain reversion, and solid-state 2H NMR of labeled guests, this work shows how relaxive impurities lower the barrier to domain switching and how differences in perfection between mother and daughter domains provide the driving force for the memory effects. Although the interfacial effects implicated here are different from the volume effects that operate in certain shape memory materials, the twinning and defect phenomena responsible for the rubber-like behavior and memory effects should be generally applicable to domain switching in ferroelastic and ferroelectric crystals and to other solid-state processes.

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Aluminum nitride (AlN) is a promising substrate material for emerging wide-bandgap electronic and opto-electronic devices. Although existing manufacturing technology is less mature than for sapphire and silicon carbide substrates, aluminum nitride has been demonstrated to be superior for deep UV lightemitting applications and may ultimately surpass silicon carbide in both cost and performance for high power RF. Advantages include the identical crystal structure and close lattice match to high Al-content nitride alloys. In addition, AlN and GaN have closely matched thermal expansions from room temperature up to typical growth temperatures. The AlN has a band-gap energy of 6.2 eV with an index of refraction of 2.2 which is attractive for the extraction of uv light and is highly insulating which is attractive for high frequency devices. We use a sublimation-recondensation approach to produce large bulk AlN single crystals. Single crystal boules 15 mm in diameter and several cm in length have been grown and native-nitride substrates with dislocation densities below 10 3 cm -2 and with a thermal conductivity exceeding 3 W/cm-K at 300K, have been obtained from those boules. Crystal IS is currently developing 50 mm diameter singlecrystal boules. 1 Introduction A new class of semiconductors with conduction band energies about 3 eV or more above the valence band (Wide-Bandgap) is bringing revolutionary performance to high-performance electronic and optoelectronic devices. These materials include silicon carbide (SiC) and alloys of gallium nitride (GaN). They offer roughly a 5-10 × improvement over silicon-and gallium arsenide (GaAs)-based electronics in that they can operate at higher temperatures, higher voltages, and higher current densities. In the case of GaN alloys, structures utilizing the piezoelectric effect offer a novel and more efficient method for concentrating charge in High Electron Mobility Transistor (HEMT) devices. Existing substrates for these applications include SiC and sapphire, but high quality, native nitride substrates have distinct advantages.GaN and its alloys are also suitable for making optoelectronic devices such as solar-blind UV detectors, UV, blue and green Light Emitting Diodes (LEDs), and visible solid state lasers. With the addition of phosphors, compact, low-voltage, solid-state white light sources are possible. Current applications include displays, small light sources (such as flashlights), and lasers for information storage. Future applications include very long lifetime, high energy efficiency (better than fluorescent) lighting, and very high density information storage from UV LEDs and lasers. Realization of these applications will benefit substantially from the development of cost-effective, native nitride substrates in analogy to the way Sibased and GaAs-based technologies have developed.While the III-nitrides (AlN, GaN and InN) are completely miscible over all alloy concentrations, there is substantial variation in the lattice parameter. That of InN is more than 10% larger than ...

Observations have been made, using synchrotron white beam x-ray topography, of stacking faults in 4H–SiC with fault vectors of kind 1/6⟨202¯3⟩. A mechanism has been postulated for their formation which involves overgrowth by a macrostep of the surface outcrop of a c-axis threading screw dislocation, with two c/2-height surface spiral steps, which has several threading dislocations of Burgers vector c+a, with c-height spiral steps, which protrude onto the terrace in between the c/2-risers. Such overgrowth processes deflect the threading dislocations onto the basal plane, enabling them to exit the crystal and thereby providing a mechanism to lower their densities.

Molybdenum (Mo)/4H-silicon carbide (SiC) Schottky barrier diodes have been fabricated with a phosphorus pentoxide (P 2 O 5 ) surface passivation treatment performed on the SiC surface prior to metallization. Compared to the untreated diodes, the P 2 O 5 -treated diodes were found to have a lower Schottky barrier height by 0.11 eV and a lower leakage current by two to three orders of magnitude. Physical characterization of the P 2 O 5 -treated Mo/SiC interfaces revealed that there are two primary causes for the improvement in electrical performance. First, transmission electron microscopy imaging showed that nanopits filled with silicon dioxide had formed at the surface after the P 2 O 5 treatment that terminates potential leakage paths. Second, secondary ion mass spectroscopy revealed a high concentration of phosphorus atoms near the interface. While only a fraction of these are active, a small increase in doping at the interface is responsible for the reduction in barrier height. Comparisons were made between the P 2 O 5 pretreatment and oxygen (O 2 ) and nitrous oxide (N 2 O) pretreatments that do not form the same nanopits and do not reduce leakage current. X-ray photoelectron spectroscopy shows that SiC beneath the deposited P 2 O 5 oxide retains a Si-rich interface unlike the N 2 O and O 2 treatments that consume SiC and trap carbon at the interface. Finally, after annealing, the Mo/SiC interface forms almost no silicide, leaving the enhancement to the subsurface in place, explaining why the P 2 O 5 treatment has had no effect on nickel-or titanium-SiC contacts.

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H–SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current–voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier height within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.