Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session D6: Materials III: Interfaces |
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Chair: R. Clayton Shallcross, University of Arizona Room: MU246 |
Friday, October 16, 2015 1:50PM - 2:02PM |
D6.00001: Design and performance of mid and long infrared III-V semiconductor superlattice materials Preston T. Webster, Arvind J. Shalindar, Nathaniel A. Riordan, Chaturvedi Gogineni, Huan Liang, Ankur R. Sharma, Shane R. Johnson The band structure and electron-hole wavefunction overlap of III-V semiconductor superlattice materials at the GaSb lattice constant is investigated for mid and long wavelength infrared applications. To facilitate the growth of arbitrarily thick pseudomorphic layers, only mole fractions and layer thicknesses that result in zero accumulated in-plane strain are considered. Despite this constraint, superlattices offer two additional free design parameters; one used to tune the ground state absorption cutoff (effective bandgap), with the other available for optimizing absorption (electron-hole wavefunction overlap) at the cutoff. In particular, the design criteria for optimal absorption as function of ground state energy is identified for lattice-matched GaSb/InAs$_{\mathrm{0.911}}$Sb$_{\mathrm{0.089}}$ and GaSb/InAs$_{\mathrm{0.932}}$Bi$_{\mathrm{0.068}}$ superlattices and strain-balanced InAs/GaInSb, InAs/InAsSb, and InAs/InAsBi superlattices on GaSb substrates. The absorption coefficient for each superlattice system is determined from spectroscopic ellipsometry measurements of InAs/InAsSb superlattices and the square of the wavefunction overlap. An increase in operating temperature results in a decrease in ground state transition energy with virtually no change in wavefunction overlap, indicating that the optimal absorption is independent of temperature. [Preview Abstract] |
Friday, October 16, 2015 2:02PM - 2:14PM |
D6.00002: Influence of Pre and Post-treatments on Plasma Enhanced ALD SiO2 and Al2O3 layers on GaN Mei Hao GaN-based transistors are projected to be the next generation power electronics due to its excellent material properties. In this research, electronic properties of the resulting interfacial oxide layer on GaN-based metal–oxide–semiconductor (MOS) devices were investigated using plasma enhanced atomic layer deposition (PEALD) dielectric layers. The goal was to reduce the leakage current through the dielectric layer. Dielectric layers of SiO2 and Al2O3 have a band gap of 9 eV and 6.5 eV respectively. It has been an expected breakdown field 10 MV/cm for Al2O3 on GaN. However, PEALD dielectric layers are very sensitive to the GaN surface before deposition. Different pre-treatments of GaN before the PEALD process can create different surface conditions, which influence the dielectric layer structure and electronic properties. In this study, the band alignment of SiO2 and Al2O3 on GaN was examined with an x-ray photo-electron spectroscopy. An N2/H2 plasma pre-treatment at 680? was employed prior to SiO2 and Al2O3 deposition, and a breakdown field of 9.9 MV/cm was found for SiO2 and 7 MV/cm for Al2O3. Moreover, a post-deposition annealing of the Al2O3 on GaN samples with different temperatures, influenced the electrical behavior, including removal of interface charges. [Preview Abstract] |
Friday, October 16, 2015 2:14PM - 2:26PM |
D6.00003: ZnTe:P/CdTe Superlattice Window for CdTe Solar Cell on InSb Substrates Ernesto Suarez, Xin-Hao Zhao, Yuan Zhao, Calli Campbell, Maxwell Lassise, Preston Webster, Shi Liu, Ying-Shen Kuo, Yong-Hang Zhang The current efficiency record of monocrystalline CdTe solar cells is significantly lower than the Shockley-Quassar limit. A primary reason for this is the unsuccessful p-type doping of CdTe, which is due to the existing dopants that are difficult to be ionized or to incorporate during epitaxial growth. Here we propose a CdTe/ZnTe solar cell with an n-type Indium doped CdTe absorber layer and a CdTe/p-ZnTe superlattice window layer. This superlattice utilizes high acceptor doping of ZnTe while reducing relaxation through the use of CdTe. Phosphorous has shown to be an effective dopant in ZnTe that can reach a 10$^{\mathrm{19}}$ cm$^{\mathrm{-3\thinspace }}$hole concentration. The window layer is designed with an average hole concentration of 1 x 10$^{\mathrm{18}}$ cm$^{\mathrm{-3}}$, an effective bandgap of 1.64 eV, and a depletion width of 4 nm. The absorber layer is 1 \textmu m thick and has an electron concentration of 1\texttimes 10$^{\mathrm{16}}$ cm$^{\mathrm{-3}}$. Between the InSb substrate and the nCdTe absorber is an nMgCdTe barrier to reduce the non-radiative interface recombination and increase the minority carrier lifetime. The theoretical efficiency of this cell is 23{\%}. Preliminary experimental results are also presented. [Preview Abstract] |
Friday, October 16, 2015 2:26PM - 2:38PM |
D6.00004: Ultra-long minority carrier lifetime and ultra-low interface recombination velocity in CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy Xin-Hao Zhao, Shi Liu, Calli Campbell, Maxwell Lassise, Yuan Zhao, Ying-Shen Kuo, Yong-Hang Zhang CdTe/MgCdTe double heterostructures (DHs) are grown on InSb (001) substrates using molecular beam epitaxy (MBE). The MgCdTe layers act as barriers to confine both electrons and holes in CdTe. The undoped intrinsic n type DHs show very high crystalline quality, strong photoluminescence, a minority carrier lifetime as long as 2.7 $\mu $s, and an interface recombination velocity as low as \textless 1 cm/s. These values are already comparable to that of the best quality GaAs/AlGaAs DHs. The effective interface recombination velocity is found to be dependent on not only the Mg composition but also the thickness of the MgCdTe layer, due to thermionic emission and tunneling effects. The CdTe/MgCdTe DH samples are also doped with indium from 1$\times $10$^{\mathrm{16}} \quad cm^{-3}$ to 5$\times $10$^{\mathrm{18\thinspace }}cm^{-3}$, and the dopants are founds to be 100{\%} ionized within the doping range from 1$\times $10$^{\mathrm{16}}$ $cm^{-3}$ to 1$\times $10$^{\mathrm{18}} \quad cm^{-3}$. Decent carrier lifetimes are achieved ($\sim $100 ns) with doping concentrations from 1$\times $10$^{\mathrm{16}} \quad cm^{-3}$ to 1$\times $10$^{\mathrm{17}}$ $cm^{-3}$, which indicates the potential application of this structure in high efficiency CdTe solar cells. [Preview Abstract] |
Friday, October 16, 2015 2:38PM - 2:50PM |
D6.00005: Electron affinity of cubic boron nitride terminated with vanadium-oxide Yu Yang, Tianyin Sun, Joseph Shammas, Manpuneet Kaur, Mei Hao, Robert Nemanich H-terminated cubic boron nitride (c-BN) has been shown to exhibit a negative electron affinity (NEA) surface, which may enable applications in thermionic and photon-enhanced energy conversion devices. The ability to withstand high temperature operation is an important factor in the thermionic emission applications. Theoretical and experimental studies have indicated that transition metal oxides can significantly influence the electronic properties of diamond. In this study, a thermally stable NEA for a c-BN surface with vanadium-oxide-termination is achieved, and its electronic structure was analyzed with \textit{in-situ} photoelectron spectroscopy. Thin vanadium layers of \textasciitilde 0.1 and 0.5 nm were deposited on the c-BN surface in an electron beam deposition system. Oxidation of the metal layer was achieved by an oxygen plasma treatment. After 650 \textordmasculine C thermal annealing, the vanadium oxide on the c-BN surface was determined to be VO$_{\mathrm{2}}$, and the surfaces were found to be thermally stable, exhibiting an NEA. In comparison, the oxygen-terminated c-BN surface, where B$_{\mathrm{2}}$O$_{\mathrm{3}}$ was detected, showed a positive electron affinity (PEA) of \textasciitilde 1.2 eV. The B$_{\mathrm{2}}$O$_{\mathrm{3}}$ evidently acts as a negatively charged layer introducing a surface dipole directed into the c-BN. Through the interaction of VO$_{\mathrm{2}}$ with the B$_{\mathrm{2}}$O$_{\mathrm{3}}$ layer, a B-O-V layer structure would contribute a dipole between the O and V layers with the positive side facing vacuum. The lower enthalpy of formation for B$_{\mathrm{2}}$O$_{\mathrm{3}}$ is favorable for the formation of the B-O-V layer structure, which provides a thermally stable surface dipole and a NEA surface. [Preview Abstract] |
Friday, October 16, 2015 2:50PM - 3:02PM |
D6.00006: Optical Properties of Si-Integrated Group-IV Light Emitting Diodes James Gallagher, Charutha Senaratne, Chi Xu, John Kouvetakis, Jose Menendez Light emitting diodes (LEDs) using GeSn and GeSiSn alloys are incorporated on Si(100) substrates using custom deposition chemistries and novel buffer layer strategies. The emission properties of these devices are studied by room temperature electroluminescence (EL) as a function of alloy composition and device architecture. The GeSn devices investigated span the range from indirect to direct gap semiconductors (0-12{\%} Sn). In the case of ternary GeSiSn diodes, two composition ranges are studied: one with fixed Si (2-3{\%}) while the Sn is varied (3-11{\%}), and the other with fixed Sn (9-11{\%}) and varying Si (3-10{\%}). The results from the former set show a transition towards direct gap materials and the latter demonstrate a blueshift of the direct gap signal to higher energies within the mid IR. The basic device design begins with a $n$-Ge contact grown on a Si substrate followed with the $i$-GeSn active layer and the $p$-GeSn top electrode. Electron microscopy of the samples reveals a defective $n$/$i$ and a defect-free $i$/$p$ interface. The $n$/$i$ defects can be eliminated by substituting a lattice matched $n$-GeSn$_{\thinspace }$material for the $n$-Ge layer producing homo-structure designs that significantly improve the emission efficiency of the LEDs. [Preview Abstract] |
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