Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S53: Nitride SemiconductorsFocus Live
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Sponsoring Units: DMP DCOMP FIAP Chair: John Lyons, United States Naval Research Laboratory |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S53.00001: Point Defect Management in III-Nitrides: A Systematic Approach Invited Speaker: Ramon Collazo Defect incorporation is dependent on the defect formation energy and hence on associated chemical potentials and the Fermi level. For example, the formation energy of CN in Al/GaN varies as the chemical potential difference (µN- µC) and -EF (Fermi level). Here, we demonstrate a systematic approach to point defect control by employing the defect formation energy as a tool through (a) chemical potential control and (b) Fermi level control. Chemical potential control (µN and µC) with a case study of C and Si in MOCVD Al/GaN is reported. We derive a relationship between growth parameters, metal supersaturation and chemical potentials of III/N and impurity atoms demonstrating successful quantitative predictions of C incorporation and other corresponding compensating defects as a function of growth conditions in Al/GaN. Hence the growth environment necessary for minimal defect incorporation within any specified constraints may be determined. Fermi level control based point defect reduction is demonstrated by modifying the Fermi level describing the probability of the defect level being occupied/unoccupied i.e. defect quasi Fermi level (DQFL). The DQFL is modified by introducing excess minority carriers (by above bandgap illumination). A predictable (and significant) reduction in compensating point defects (CN, H, VN, VIII-nSi) in (Si, Mg) doped Al/GaN measured by electrical measurements, photoluminescence and secondary ion mass spectroscopy (SIMS) provides experimental corroboration. Further, experiments with varying steady state minority carrier densities at constant illumination prove the role of minority carriers and DQFL in defect reduction over other influences of illumination that are kept constant. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S53.00002: Plasma frequency in doped highly mismatched alloys Hassan Allami, Jacob J Krich Group III-nitride alloys are the prototypical examples of highly mismatched alloys (HMA), where the alloying element with significantly different electronegativity (e.g., nitrogen) forms localized defect states. These defect states couple to extended states of the host semiconductor and create two split bands; the lower split band has been used as an intermediate band for intermediate band solar cells. We consider a HMA with such a conduction band anticrossing where the lower split band is partially filled by doping. The mobile electrons in the lower band sustain plasmonic oscillations, and we show that they behave differently than their counterparts in metals and semiconductors due to the anomalous state distribution in the split bands of HMAs. We use a spectral density for HMAs to build a model that allows study of the effects of the state distribution on the bulk plasma frequency. We solve our model semi-analytically and show that interband effects of the upper split band bound the plasma frequency to be smaller than an effective band gap. We focus on GaAsNP quaternaries and show their special appeal for mid-infrared plasmonic applications due to their high tunability and the presence of an energy gap between the two split bands. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S53.00003: Influence of Surface Treatments on the Structure of GaN Layers Jiaheng He, GuanJie Cheng, Zhirong Zhang, Maggie Chen, Sam Frisone, Alexandra Zimmerman, Fabian Naab, Sizhen Wang, Bingjun Li, Jung Han, Rachel Goldman Although silicon-based electronics are used to power light-emitting diodes and electric vehicles, their utility in high power applications is limited by slow switching and high on-state resistance. The most promising alternatives are vertical GaN devices, but these require etching and selective-area re-growth that may displace surface and near-surface Ga and N atoms. To understand processing-structure-property relationships relevant to vertical GaN devices, we examine the influence of dry etching and metal-organic (MO) precursor treatment on the structure and properties of GaN substrates and epitaxial GaN layers. For these studies, we visualize the crystal symmetry/orientation using 2D planar ion channeling maps and angular yield profiles collected with a fully-automated 5-axis goniometer recently attached to the endstation of the 1.7 MeV Tandetron at the Michigan Ion Beam Laboratory. Our results suggest that the MO precursor reduces the density of displaced surface Ga atoms. To quantify the concentration and distribution of displaced atoms, we will compare 2D ion channeling maps with 2D Monte Carlo-Molecular Dynamics simulations using Flux 7.9.6. We will also present 2D maps of elastic recoil detection analysis spectra to evaluate the spatial distribution of H. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S53.00004: Evidence of new point defects optical features in Zr-implanted polycrystalline AlN films Azin Aghdaei, Rajesh Pandiyan, Bouraoui Ilahi, Martin Chicoine, Mohamed El Gowini, François Schiettekatte, Luc G. Frechette, Denis Morris Recently negatively charged nitrogen vacancies and large metal ion (Zr, Hf) – vacancy pairs in aluminum nitride (AlN) have been theoretically reported as promising qubit candidates [1]. In this work, we have investigated the impact of thermal annealing gaseous atmosphere of argon, nitrogen, and forming gas on the structural and optical properties of thin polycrystalline AlN films subjected to high-energy implantation of zirconium ions. The results from structural characterizations suggest that the structural and morphological properties of the Zr-implanted AlN films depend on the annealing gaseous environment. A series of absorption and emission bands were observed using photoluminescence spectroscopy (PL) and photoluminescence excitation spectroscopy (PLE). The origin of the emission or absorption bands is identified and attributed to various types of point defects and defect complexes theoretically reported for AlN. New emission and absorption peaks at 1.7 eV (730 nm) and 2.6 eV (466 nm), respectively, have been identified and attributed to the (ZrAl-VN)0 defect complexes. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S53.00005: Color tunability of light-emitting diodes based on Eu-doped GaN active layers Hayley Austin, Kelsey Ortiz, Brandon Mitchell, Jun Tatebayashi, Yasufumi Fujiwara, Volkmar R G Dierolf In the pursuit of color-tunable single-pixel LEDs, it has been demonstrated that under current injection, a Europium-doped Gallium Nitride (GaN:Eu) device can be tuned from red to orange to yellow by adjusting the duty cycle and amplitude of pulse-width modulated pulsed excitation. The underlying process is a redistribution of excitation by the re-excitation of already excited centers. To further study the underlying processes, modeling has been performed by considering a local defect complex consisting of a trap for carriers and a Eu ion. The transfer of energy within the defect complex is modeled with a rate equation approach using experimentally determined constants such as transfer rates and lifetimes. Different pulse sequences and carrier densities per unit time are used to simulate experimental conditions. The model predicts the relative average populations of the Eu’s 5D0 and 5D1 states. These populations can be related to chromaticity using the color mixing of the red emission from the 5D0 state with green emission originating from the 5D1 state in order to predict the generated color. We present a comparison of the predicted and experimentally observed behaviors and discuss extensions of the model and possibilities to extend the color coverages of the single-pixel LED. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S53.00006: Alloy-Limited Electron Mobility of AlGaN Evaluated by Unfolding the DFT Band Structure Nick Pant, Zihao Deng, Emmanouil Kioupakis Alloy scattering is the dominant scattering mechanism in the AlxGa1-xN alloy system. AlGaN is an ultrawide bandgap semiconductor with promise in deep-ultraviolet LEDs for disinfection and energy-efficient high-power transistors. In this work, we evaluate the intrinsic limit to the low-field electron mobility of AlGaN from first principles. We introduce a method to calculate the quantum scattering lifetime, which appears as an energy broadening in the band structure, by unfolding the band structure from the supercell basis to the primitive-cell basis. We fit a model scattering potential to the first-principles scattering rate data and evaluate the low-field electron mobility using the semiclassical Boltzmann transport equation in the relaxation-time approximation. Our calculated mobility is in agreement with experimental values. The lowest alloy-scattering electron mobility, across the entire composition range of AlGaN, is 186 cm2/Vs, which is comparable to the highest electron mobility predicted in the competitor system (AlxGa1-x)2O3. Our method can be extended, in the future, to alloys that exhibit preferential atomic ordering and to other types of defect scattering. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S53.00007: Semiconducting character of LaN: magnitude of the band gap, and origin of the electrical conductivity Zihao Deng, Emmanouil Kioupakis Lanthanum nitride (LaN) has attracted research interest due to its promise in enabling efficient and cost-effective synthesis of ammonia from N2 gas. Despite exciting progress in the field, the electronic character of LaN (metallic, semi-metallic, or semiconducting) has not been conclusively determined. We investigate the electronic and defect properties of LaN with hybrid DFT calculations. In contrast to previous claims that LaN is semi-metallic, our calculations show that LaN is a direct-gap semiconductor with a band gap of 0.75 eV. Nitrogen vacancies and substitutional oxygen atoms are two unintentional shallow donors with low formation energies that can explain the origin of the observed electrical conductivity. Our calculations clarify the semiconducting nature of LaN and reveal candidate point defects that can explain its measured electrical conductivity. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S53.00008: Defect engineering on demand in GaAsN nanowires by post-growth hydrogen irradiation Nadine Gächter, Elena Blundo, Mitsuki Yukimune, Ilaria Zardo, Fumitaro Ishikawa, Antonio Polimeni, Marta De Luca In bulk and nanostructured semiconductors, the optical properties are usually engineered by varying crystal growth conditions or by applying high strain levels. Here, we report post-growth band-structure engineering in nanowires by mere exposition to low-energy ionized hydrogen gas. Our GaAs/GaAsN core/multishell nanowires contain 0.7%, 2% and 3% N [1]. At these low concentrations (typical of dilute nitrides), N atoms behave as strongly localized and perturbing lattice defects, and give rise to a number of counterintuitive effects. Among others, we observe a giant red-shift of the GaAsN bandgap as high as 0.5 eV with increasing N from 0 to 3%. We demonstrate that these defects can be engineered on demand, as the hydrogenation allows to passivate N by forming N-H complexes and thereby tune the GaAsN bandgap up to the value of the GaAs [2]. This N passivation is accompanied by a photoluminescence signal increase of more than an order of magnitude. The approach creates new, fast and effective possibilities for tuning the optical properties of nanowires at the nanoscale and forming highly efficient site-controlled quantum dots at telecom wavelengths. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S53.00009: Predictions for Yellow Luminescence In Cubic GaN Under Hydrostatic Pressure Arthur Edwards, Peter Schultz, Richard Dobzynski, Renee M. Van Ginhoven, Andrew C Pineda
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Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S53.00010: Weak localization in compositionally graded AlxGa1-xN Abdullah Shafe, Athby Al-Tawhid, Pegah Bagheri, Pramod Reddy, Seiji Mita, Baxter Moody, Ramon Collazo, Zlatko Sitar, Kaveh Ahadi We report on the observation of weak localization in the compositionally graded AlxGa1-xN. The polar discontinuity at the epitaxial interface of dissimilar nitrides could introduce a two-dimensional electron gas. Compositionally graded structures, however, could introduce similar sheet carrier density distributed across the film. The various heterostructures were grown on AlN single crystal substrate using metal-organic chemical vapor deposition. The concentration of aluminum was graded, from x=0.56 to x=1, uniformly across the film thickness. The Hall resolved carrier density (1.35×1018 cm-3) closely matches the theory predicted values, hinting an extremely low density of compensating defects. Room temperature capacitance measurements reveal a three-dimensional distribution of charge carriers. The sheet resistance shows a metallic behavior (dRs/dT>0) with negligible Hall carrier freeze-out, cooling down to helium liquid temperature. Signatures of the weak localization were observed in the longitudinal magnetoresistance below 30 K. The magnetoresistance shows a well-known parabolic behavior at higher temperatures. The low-temperature longitudinal magnetoresistance shows good agreement a two-dimensional weak localization model, suggesting a dimensional crossover with temperature. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S53.00011: Doping-limitations of cubic boron nitride: effect of unintentional defects on shallow doping Tamanna Joshi, Pankaj Kumar, Bipul Poudyal, Sean Russell, Pratibha Dev Cubic boron nitride (cBN) is an ultra-wide bandgap material with potential for extreme temperature and pressure applications. Although, a p-n junction using this material was demonstrated almost three decades ago, full potential of cBN in device applications has not been realized. Two main hurdles are difficulties in producing high-quality cBN films and controllable n- and p- doping its matrix. In this theoretical work, we study the reasons for doping-limitations, an acute issue in realizing cBN-based electronics. We find that different intrinsic and extrinsic defects act as compensating defects and/or introduce trap states. Amongst different foreign impurities, we explored defects containing carbon and oxygen, as large numbers of these impurities are detected in as-grown cBN. We find that the unintentional defects and their complexes not only affect the incorporation of the shallow dopants [silicon and beryllium], but also can introduce deep trap states, which will adversely affect cBN-based devices. Our analysis of doping-limitations due to unintentional defects/impurities is an important step towards finding solutions for controllably n- or p-doping cBN. |
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