Photoluminescence (PL) studies of bulk and epitaxial CdTe samples obtained from several sources are discussed. Steady state PL measurements were carried out at temperatures ranging 16–300 K. The effects surface preparation, substrate temperature, film thickness studied in detail for homoepitaxial films grown on the (111)A (100) planes CdTe. (0001) sapphire by molecular beam epitaxy (MBE), hot wall MBE, metal-organic chemical vapor deposition (MOCVD), (111)B GaAs MBE have also been completed....

Magnetotransport measurements and x-ray photoemission spectroscopy were used to investigate the surface conductivity of ZnO. Near-surface downward band bending, consistent with electron accumulation, was found on polar nonpolar faces bulk ZnO single crystals. A significant polarity effect observed in that bending consistently stronger Zn-polar face weaker O-polar face. The accumulation layer significantly influence electrical properties high resistivity, hydrothermally grown crystals at...

The optical properties of polycrystalline CdTe films prepared using vacuum sublimation techniques are discussed. Refractive index measurements reported for the wavelength region 450–2000 nm and compared with single-crystal values. Extinction absorption coefficient strong regime (450–900 nm). uv reflectance also New structure in many film samples is attributed to stacking sequence changes which introduce elements hexagonal phase. X-ray diffraction results support this conclusion. data...

Homoepitaxial GaN films, doped with Mg, were grown by rf-plasma molecular-beam epitaxy on Ga-polarity (0001) templates. Convergent-beam electron diffraction analysis establishes that the film polarity changes from [0001] to [0001_] when Mg flux during growth is approximately 1 ML/s. Secondary ion mass spectrometry indicates a doping concentration of ∼1020 cm−3 in where inversion occurs, and reduced incorporation material. Transmission microscopy shows domain boundary faceted predominantly...

Variable magnetic field Hall effect, photoluminescence, and capacitance-voltage (CV) analysis have been used to study InN layers grown by plasma assisted molecular beam epitaxy. All three techniques reveal evidence of a buried p-type layer beneath surface electron accumulation in heavily Mg-doped samples. Early indications suggest the Mg acceptor level may lie near 110meV above valence band maximum. The development doping offers great promise for future based devices.

Results of initial attempts to grow cubic-phase CdTe films on sapphire by molecular beam epitaxy are reported. Depositions have been completed (11̄02) R-plane, (12̄10) A-plane, and (0001) basal plane substrates. Substrate temperatures in the range 260–350 °C were employed along with deposition rates 1.5–7.5 Å/s. generally produced containing some elements hexagonal phase, as disclosed x-ray diffraction UV reflectance measurements. Sharp was obtained for thick (∼5 μm) grown The epitaxial...

A pronounced dependence of Mg incorporation on surface polarity was observed in a series step-doped epitaxial GaN layers grown by rf-plasma-assisted molecular-beam epitaxy. Incorporation studied for both (0001), or Ga-polarity and (0001̄) N-polarity orientations. Up to factor 30 times more incorporated under certain conditions, as determined secondary ion mass spectrometry. Measurements indicate accumulation occurs during growth, with stable accumulations close monolayer the surface. The...

GaN was grown by molecular beam epitaxy using an rf plasma source. Growth under gallium-rich conditions at 730 °C required to produce high quality layers as indicated photoluminescence, Hall effect, atomic force microscopy, and x-ray diffraction measurements. Atomic hydrogen has a significant effect for Ga-rich growth, increasing growth rates much factor of 2.

We report the successful p-type doping of CdTe films with arsenic using photoassisted molecular beam epitaxy growth technique. These doped epilayers were grown at substrate temperatures as low 180 °C. The room-temperature hole concentrations in CdTe:As layers ranged from 7×1015 to 6.2×1018 cm−3 determined by van der Pauw–Hall effect measurements. propose a mechanism responsible for high levels observed films. acceptor ionization energy was found ∼58–60 meV low-temperature photoluminescence

Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence photoluminescence (PL) on both excitation intensity time. The measured PL characteristics, interface state density extracted modeling, indicate that efficiency CdMgTe/CdTe DHs is comparable AlGaAs/GaAs DHs, with densities in low 1010 cm−2 carrier lifetimes...

We show that Be exhibits amphoteric behavior in GaN, involving switching between substitutional and interstitial positions the lattice. This is observed through dominance of ${\mathrm{Be}}_{\mathrm{Ga}}$ positron annihilation signals Be-doped while emergence ${V}_{\mathrm{Ga}}$ at high temperatures a consequence impurities being driven to positions. The similarity this found for Na Li ZnO suggests could be universal property light dopants substituting heavy cations compound semiconductors.

The electron and positron magnetic moments are the most precise prediction of standard model particle physics. accurate measurement a property an elementary has been made to test this result. A new experimental method is now being employed in attempt improve accuracy by order magnitude. Positrons from “student source” suffice for experiment. Progress toward summarized.

Growth of GaN by rf-plasma molecular beam leads to different surface morphologies for nitrogen-rich growth versus gallium-rich growth. Nitrogen-rich produces a significant density pyramidal hillocks while results in flat surfaces. Differences morphology were directly linked the presence inversion domains which originated nucleation layer. and under atomic hydrogen enhanced rate with respect surrounding matrix, Ga-rich conditions resulted more nearly equal rate.

Currently, only one shallow acceptor (Mg) has been discovered in GaN. Here, using photoluminescence (PL) measurements combined with hybrid density functional theory, we demonstrate that a effective-mass state also exists for the ${\mathrm{Be}}_{\mathrm{Ga}}$ acceptor. A PL band maximum at 3.38 eV reveals level $113\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{meV}$ above valence band, which is lowest value among any dopants GaN reported to date. Calculations suggest dual-nature...

High-quality (0001) and (0001̄)-GaN films were grown by plasma-assisted molecular-beam epitaxy to study the dependence of oxygen incorporation on polarity partial pressure. Oxygen incorporates at a rate ten times faster nitrogen-polar GaN than Ga polarity. doping is controllable, reproducible, produces low compensation material up concentrations least 1018 cm−3 with higher levels showing significant compensation. Layers containing above 1022 exhibit severe cracking while less 1021 do not...

Surface reconstructions during homoepitaxial growth of GaN (0001) are studied using reflection high-energy electron diffraction and scanning tunneling microscopy. In agreement with previous workers, a distinct transition from rough to smooth morphology is seen as function Ga N ratio growth. However, in contrast some prior reports, no evidence for 2×2 reconstruction observed. Observations have been made four different nitrogen plasma sources, similar results each case. A structure the surface...

Results of initial attempts to grow cubic-phase CdTe films on (111) and (100) Si substrates by molecular beam epitaxy are reported. Substrate temperatures in the range 200–400 °C were employed along with deposition rates 1–9 Å/s. Films grown at below 300 exhibited streaked x-ray diffraction patterns which contained extra hexagonal-phase features. Sharp was obtained for 330–350 °C. Similar depositions also produced epitaxial films. However, epilayers displayed unusual suggestive twin...

A systematic study of CdTe film growth by molecular beam epitaxy (MBE) on hydroplaned (111)A and (111)B substrates is discussed. Substrate preparation prior to involved chemical etching techniques, rather than sputtering in UHV, order maintain the integrity surface. range substrate temperature during was investigated. X-ray diffraction, UV reflection, transmission electron diffraction measurements were employed evaluate structural quality films. Bright dark field microscopy used determine...

A reduced growth rate for plasma-assisted molecular beam epitaxy of GaN often limits to temperatures less than 750 °C. The reduction can be significantly larger expected based on thermal decomposition. Conditions producing a flux consisting predominantly either atomic nitrogen or metastables have been established using various radio-frequency sources. use nitrogen, possibly coupled with the presence low-energy ions, is associated premature decrease in rate. When active consists primarily...

By using density functional calculations in the generalized gradient approximation, we investigate energetics of Mg adsorption and incorporation at GaN(0001) $\mathrm{Ga}\mathrm{N}(000\overline{1})$ surfaces under various Ga coverage conditions as well presence light or electron beam-induced electronic excitation. We find significant differences between Ga- N-polar surfaces. is easier Ga-polar surface, but high coverages are found to cause important distortions which locally change polarity...

Density functional theory calculations of oxygen adsorption and incorporation at the polar $\mathrm{GaN}(0001)$ $\mathrm{GaN}(000\overline{1})$ surfaces have been carried out to explain experimentally observed reduced concentration in $\mathrm{GaN}$ samples grown by molecular beam epitaxy presence high energy $(\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{keV})$ electron irradiation [Myers et al., J. Vac. Sci. Technol. B 18, 2295 (2000)]. Using a model which effect is excite...

Illumination of the substrate during growth by molecular-beam epitaxy (MBE), known as photoassisted epitaxy, has been investigated for (111)B, (211)B, and (100) oriented HgCdTe on CdZnTe. The results this investigation indicate that MBE in significant improvements structural perfection. epilayers with average double-crystal x-ray diffraction full widths at half-maximum <30 arc s can be obtained all three orientations. Dislocation line densities low 5×104 cm−2 have observed....

Epitaxial YMnO3 films were grown on (0001) GaN-on-sapphire templates using molecular beam epitaxy. The maintained the orientation with an in-plane YMnO3∕GaN epitaxial relationship of (0001)‖(0001); [11¯00]‖[112¯0]. was ferroelectric at room temperature a remanent polarization ∼3.2μC∕cm2 and saturation ∼12μC∕cm2. This heterostructure is promising candidate for multifunctional structures that integrate ferroelectrics GaN-based high-power short-wavelength light-emitting devices.

Photoluminescence spectra were obtained at 77 K for three undoped CdTe single crystal specimens whose surfaces prepared by mechanical, conventional chemimechanical, and modified hydroplane polishing techniques, respectively. The polished sample was found to be a much brighter source of photoluminescence than either the other two specimens. In addition, produced spectrum in which nearly all emission occurred band centered 1.58 eV rather well-known defect 1.42 eV. We interpret these results as...