Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K11: Dopants and Defects in Semiconductors - NitridesFocus
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Sponsoring Units: DMP DCOMP FIAP Chair: Grace Xing, Cornell University Room: LACC 303A |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K11.00001: Identifying the source of deep defect luminescence bands in AlN and GaN: Slowly decaying DX center related emissions Invited Speaker: Klaus Thonke The direct semiconductors AlN and GaN are the materials of choice for optoelectronic applications in the VIS to UV range, but are still hampered by high densities of crystalline defects and a lack of control on unintentional dopants. Especially for AlN, typically broad photoluminescence emission bands are observed over the whole photon energy range from 1.4 – 4.5 eV. |
(Author Not Attending)
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K11.00002: Defect Level of a C-Related Center in C-Doped GaN Subash Paudel, William Willoughby, Mary Zvanut, M. Bockowski, M. Iwinska, T. Sochacki High-power applications of GaN require semi-insulating substrates, which can be obtained by incorporation of impurities like carbon. We used electron paramagnetic resonance (EPR) to investigate point defects in 0.2 mm thick free-standing GaN grown by hydride vapor phase epitaxy doped with 1017-1019 cm-3 carbon. The amplitude of a nearly isotropic signal with g ~ 1.987 increased with carbon concentration suggesting that the defect is related to the impurity. Photo-EPR was performed at 3.5 K on the mostly heavily doped samples. The signal increased with photon energy greater than 2.75 ± 0.15 eV. Subsequent illumination of the photo-excited center revealed that the intensity began to decrease at 0.95 ± 0.05 eV. Considering temperature dependent Hall measurements which indicate a hole activation energy of 1 eV, we interpret the 0.95 eV threshold as the energy required to excite electrons from the valance band to the defect, and conclude that the EPR detected center is responsible for compensation. The dependence of the EPR intensity on carbon concentration further suggests that the defect is C-related, perhaps substitutional carbon, in agreement with the theoretically predicted defect level of 0.9 eV. |
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K11.00003: Calcium Impurities as Nonradiative Recombination Centers in InGaN Jimmy Shen, Darshana Wickramaratne, Chris Van de Walle Recent experimental work [1] discovered high concentrations of Ca in the active layer of GaN-based light emitting diodes grown by molecular beam epitaxy. The presence of Ca was correlated with a significant reduction in the efficiency of light emission. We have used first-principles calculations to examine the mechanisms by which Ca causes defect-assisted nonradiative recombination, often called Shockley-Read-Hall (SRH) recombination [2]. Calcium substituted on the cation site turns out to be a strong recombination center. Using hybrid density functional calculations we find that substitutional Ca acts as a deep acceptor with a level ~1 eV above the GaN valence-band maximum. Based on calculated nonradiative recombination rates we find that for Ca concentrations of 1017 cm-3, the SRH recombination coefficient A in InGaN exceeds 106 s-1 for band gaps less than 2.5 eV. A coefficients of this magnitude lead to significant reductions in the efficiency of LEDs. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K11.00004: Transient Hall Effect characterization of persistent photo-generated carriers in GaN/AlGaN heterostructures David Daughton, BoKuai Lai, Jeffrey Lindemuth We report on the transient conductivity and scattering of charge carriers generated by photo-ionization of deep-level defects in GaN/AlGaN heterostructures grown on silicon and sapphire substrates. Under sub-bandgap (455 nm) illumination, photo-generated carriers increase the conductivity of on-silicon devices while, due to enhanced carrier-carrier scattering, on-sapphire devices show a conductivity decrease. After the illumination has been removed, the photo-induced carrier concentration persists for hours to days in these materials. Queisser-like logarithmic decay kinetics were observed for the on-sapphire devices at room temperature while the on-silicon devices display a more complex decay transient indicative of serial or multichannel decay mechanisms. In this work, a novel Hall effect acquisition methodology removes offset voltages from the Hall signal without the need for magnetic field reversal enabling acquisition of the Hall voltage at millisecond timescales. Carrier scattering rates were extracted by subsequent measurement of the transient conductivity. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K11.00005: Study of proton irradiation-induced effects on electrical and optical characteristics of AlGaN/GaN epi-structures Min Khanal, Kosala Yapabandara, Vahid Mirkhani, Tamara Isaacs-Smith, Benjamin Schoenek, Shiqiang Wang, Sunil Uprety, Ayayi Ayhi, Sarit Dhar, Michael Bozack, Minseo Park Due to their crystal structure and inherent properties of AlGaN and GaN, the AlGaN/GaN high electron mobility transistors (HEMTs) are the highly promising candidates for electronic applications in the harsh conditions such as high voltage, high frequency, high power and the hostile radiation environments in the space. It is necessary to have a clear understanding of the radiation effects on the materials/devices and investigate the failure mechanisms before the successful deployment of their applications. In the present research, the effects of 100 keV proton irradiation at 1E10, 1E12 and 1E14 fluences on AlGaN/GaN epi-structures grown on Si wafers were studied. The degradation of electrical characteristics and shift in the threshold voltage was observed from the irradiated samples. The optical properties of the material were analyzed by Raman and PL spectroscopy. The change in the surface morphology of the samples after irradiation was confirmed by atomic force and scanning electron microscopic analyses. The compositional analysis was performed using X-ray photoelectron spectroscopy. Electrical characteristics of the device were analyzed using conventional transistor I-V measurements. Details of the experimental methods and the analysis of the results will be presented. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K11.00006: First-Principle Investigation of Vacancy Effect on the AlInN Electronic Properties Md Golam Morshed, Chee-Keong Tan Group III-Nitride semiconductors have been extensively studied for solid state lighting applications as well as power and communications applications. Particularly recent interests emerge to employ AlInN/GaN transistors in the space environment. However, the electronic systems employing III-Nitride transistors are exposed to fluxes of radiation sources such as proton, neutron and gamma rays, leading to material degradation that significantly affects the performance. Recent work revealed creation of vacancies and dislocations in AlInN materials after irradiation of heavy ions, but vacancy effect onto the material properties is not well understood. Investigating the properties of III-Nitride materials with vacancies is thus important to advance the understanding of radiation effect on the materials. In this work, we present the analysis of electronic properties of AlInN alloy with vacancies using the First-Principle Density Function Theory (DFT) calculations. The effect of single and cluster vacancies in AlInN are analyzed. Our findings show that the vacancies in AlInN alloy result in significant changes to the band structure including the band gap and effective mass. The effect of vacancy onto the electronic properties of AlInN alloys will be further discussed in detail. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K11.00007: Strategies for p-type doping in ZnGeN2 Nicholas Adamski, Darshana Wickramaratne, Zhen Zhu, Chris Van de Walle ZnGeN2 is a direct wide-band-gap earth-abundant semiconductor that is a candidate material for optoelectronic devices. To leverage the properties of ZnGeN2 in devices requires strategies for identifying candidate dopants that can be introduced in a controlled manner. Using density functional theory with a hybrid functional, we study the role of group-III and group-I elements as candidate acceptors. We show that substitutional Al on the Ge site is the most promising acceptor, with a level 0.24 eV above the valence-band maximum, similar to the ionization energy of the Mg acceptor in GaN. However, self-compensation due to Al substitution on the Zn site is expected to be strong. We also explore the role of hydrogen complexes with the group-III elements and identify strategies for hydrogen-assisted p-type doping of ZnGeN2. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K11.00008: Native Defects and Impurities in the Wide Band Gap II-IV Nitride MgSiN2 Mikael Rasander, Michelle Moram The Group II-IV nitride semiconductors are emerging as promising alternatives to III-nitrides in ultraviolet LED applications. These materials have wurtzite-derived orthorhombic crystal structures and can be obtained by substituting pairs of Group III atoms in a III-nitride for a single Group II atom and a single Group IV atom. MgSiN2 has been shown to have a large band gap, of similar size as the band gap in wurtzite-structured AlN, and a crystal structure which would make incorporation of MgSiN2 into existing nitrides technology possible, for example in ultra-violet light-emitting diodes.[i] Here we will present results related to native as well as impurity defects in MgSiN2 obtained using hybrid density functional calculations. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K11.00009: Defects and doping in ZnGeN2: interstitials and p-type candidates Dmitry Skachkov, Walter Lambrecht The defect physics in ternary ZnGeN2 may be expected to be more complex than in binary nitrides. In a previous study we found that among the native defects, antisites ZnGe and GeZn have low energy of formation, and predict the material to be intrinsically slightly p-type. This opens questions about what is the origin of the usually found n-type doping and how to effectively p-type dope the material. In this study, we examine interstitial defects and consider some candidates for p-type doping using the FP-LMTO supercell approach along with LDA+U corrections of the gap. We find that the interstitials have higher energy of formation but present nonetheless interesting physics. While Zni is a shallow donor with a Zn-s like resonance in the conduction band, Gei has a deep Ge-s level in the gap. Ni prefers a split interstitial configuration with states related to the N2 molecule. As far as p-type dopant candidates, we consider Ga, which however suffers from antisite compensation between GaGe acceptor and GaZn donor behavior. Cu prefers the Zn over the Ge or interstitial sites but is nonetheless a deep acceptor. C prefers the N site over Ge or Zn sites but again provides a rather deep level at about 0.7 eV above the VBM. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K11.00010: Strain Effects: Properties of Deep Defects in Hexagonal Boron Nitride Olasunbo Farinre, Evan Folk, Pratibha Dev The spin states of different point defects and defect-complexes within layered semiconductors, such as hexagonal boron nitride (hBN), are of interest for different quantum applications. Using first principles-based methods, we show that strain can affect the structural, electronic and spin properties of defects such as boron and nitrogen vacancies, as well as anti-site defects within hBN monolayers. The results show that along with the defect-defect interactions, strain changes the spin-states of the defect. In particular, in the case of boron vacancy, where the unstrained structure undergoes Jahn Teller distortion, strain makes the symmetric, undistorted structure metastable. The distorted boron-vacancy defect is a spin-1/2 structure, while the symmetric structure has a net spin of 3/2. These results are promising and show that strain can be an important mechanism in manipulating the electronic and spin properties of defects in layered materials. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K11.00011: Cubic Boron Nitride on Semiconducting Diamond and its Application to Neutron Detection Jesse Brown, Yu Yang, Joseph Shammas, David Smith, Franz Koeck, Robert Nemanich We have successfully deposited cubic boron nitride (c-BN) on nitrogen doped, polycrystalline diamond and boron doped, single crystal diamond, using plasma enhanced chemical vapor deposition (PECVD) employing fluorine chemistry. In situ X-ray photo spectroscopy (XPS) was utilized to characterize the sp3 bonding structure of c-BN. Cubic boron nitride is the zinc-blende analog to diamond, which is now being considered as an ideal material for radiation detection. TEM measurements demonstrate local epitaxy for c-BN on polycrystalline diamond. Boron containing materials are particularly relevant to detecting neutrons because of their large cross section to neutron capture and alpha particle emission. Moreover, diamond and c-BN have similar lattice constant and optical band gap which enables an integrated detector design. We present an approach to deposit c-BN on the p-type layer of a PIN diamond device in order to create a neutron detector. With the similar structural and outstanding thermal properties of c-BN and diamond, these devices can be used in a variety of applications, including high temperature environments. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K11.00012: Predicting properties of Zn1+xSn1-xN2-2xO2x: defects and disorders Jie Pan, Jacob Cordell, Andriy Zakutayev, Stephan Lany ZnSnN2 (ZTN) is a promising absorber material for photovoltaic (PV) applications. However, in practice, the growth of ZTN thin film incorporates non-trivial amount of oxygen. The excess amount of oxygen can lead to cation off-stoichiometry, such as Zn excess (Zn1+xSn1-xN2-2xO2x), and disorders in the material. As a result, it becomes essential to investigate the effects of these complications to materials properties, such as optoelectronic properties, and their implications for PV devices. In this contribution, we will present our computational studies of defects and disorders in Zn1+xSn1-xN2-2xO2x (ZTNO), and their relations to materials properties, such as defect phase diagram, net doping, band gap, carrier localization, and absorption coefficients. The disordered ZTNO structures were created by motif-based Monte Carlo (MC) simulations. The MC generated structures were then passed to density functional theory (DFT) based calculations for the study of oxygen content induced changes in the electronic structures. The defect phase diagram was calculated through a DFT based thermodynamic simulation with a consideration of oxygen-induced band edge shifts. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K11.00013: Defects in N-Rich, Si-Rich, and Stoichiometric Silicon Nitride Thin Films Observed Using Electrically Detected Magnetic Resonance and Near-Zero Field Magnetoresistance Ryan Waskiewicz, Michael Mutch, Patrick Lenahan, Sean King We utilize near-zero field magnetoresistance (MR) and electrically detected magnetic resonance (EDMR) to investigate electronic transport in thin films of N-rich, Si-rich, and stoichiometric silicon nitride films. We compare EDMR and MR detected through spin dependent trap assisted tunneling (SDTAT) over a range of biasing conditions. The EDMR measurements were made at several very different field/frequency combinations, exploiting the near field and frequency independence of the EDMR response. The multiple field/frequency comparisons allow us to some extent to separate spin orbit coupling and hyperfine interaction contributions to the spectra. The multiple frequency EDMR results also provide insight with regard to the near-zero field MR response. Additionally, the MR and EDMR response as a function of bias provides (relatively crude) insight into the energy levels of the defect centers. |
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