The IV-VI semiconductor family of PbSe-SnSe alloys spans narrow direct bandgap materials in the Pb-rich cubic rocksalt phase, and indirect bandgap semiconductors in the Sn-rich layered orthorhombic phase. In recent years, there is growing interest in harnessing electronic and photonic properties of these orthorhombic phases that merit their study as epitaxial thin films. Specifically, there is excitement in harnessing in-plane ferroelectricity in SnSe demonstrated in the single or odd number bilayer limit [1]. Additionally, research groups are showing a large contrast in electronic and optical properties for phase-change devices across the orthorhombic to rocksalt structural transition that can not only be driven by temperature but also most by direct application of intense light-fields [2,3]. The development of growth recipes to fabricate high quality thin films of not only SnSe but also Pb1-xSnxSe offers new compositional routes to tune these properties. In this work, we synthesize Pb1-xSnxSe epitaxial films in the orthorhombic phase across a large composition range by molecular beam epitaxy, on technologically relevant III-V GaAs substrates. Importantly, we find it possible to stabilize metastable single phase compositions beyond what is expected in the bulk. A Riber Compact 21 MBE system with compound PbSe and SnSe cells is used to grow films. (001)-oriented semi-insulating GaAs substrates are prepared by desorbing the surface oxide under a Se overpressure, followed by PbSe surface preparation steps. We find that smooth, out-of-plane single oriented SnSe films result both from samples grown with a PbSe dose, and samples grown with a PbSe dose and buffer layer. We expand on the successful growth of SnSe on GaAs and use the identified surface preparation methods to grow orthorhombic Pnma space group Pb1-xSnxSe alloys on GaAs [4]. The Pb1-xSnxSe alloy composition is determined by the relative fluxes of the PbSe and SnSe compound cells. XRD results are used to extract orthorhombic lattice constants as a function of alloy composition, at room temperature. The difference in unit cell volume between alloys around XSn=0.5 and the predicted unit cell volume of similar composition Pb1-xSnxSe alloys in the cubic phase is small, implying a small energy cost to a phase transition at these intermediate compositions. In addition to structural properties, we will be reporting on the optical bandgap as a function of alloy composition. Based on the bulk phase diagram of the PbSe-SnSe system, we expect alloy compositions from XSn=0.4-0.8 to be two phase; both cubic and orthorhombic. The XSn=0.64 sample is phase separated. However, we have managed to grow thin film samples at XSn=0.55 and XSn=0.74 which are purely orthorhombic. Moreover, these are not the only metastable sample that we have produced in this materials system. We have synthesized room-temperature stable orthorhombic Cmcm phase of Pb1-xSnxSe , a phase typically only stable above 700 K. We will be exploring the structural properties of these samples further, including temperature cycling experiments to better understand the stability of these phases in the thin film limit. [1] C. Kai, et al. …S.S. Parkin, Nano letters, 20, 6590,(2020). [2] T. Katase et al. ... T. Kamiya, Science advances, 7(12), (2021). [3] Y. Huang, ... M. Trigo, Physical Review X, 12(1), (2022). [4]B. Haidet et al. ... K. Mukherjee, Phys. Rev. Mater., 4, 033402 (2020).

Single-Phase Orthorhombic SnSe-PbSe Alloy Thin Films Stabilized on GaAs by Molecular Beam Epitaxy

The mid-infrared wavelength range (3 -30 um, mid-IR) is a spectral range of significant importance. The mid-wave infrared (MWIR, 3 -5 um) transmission window, specifically, is vital for applications such as gas sensing and free-space communication, as well as thermal imaging of mechanical objects (engines, turbines, etc) that have temperatures ~580-970 K. For an infrared detector, efficient operation at high temperatures is typically the primary goal. While Mercury-Cadmium-Telluride (HgCdTe) detectors are the current state-of-art infrared detectors, the type-II superlattices (T2SLs) have shown to be a promising alternative material system. However, the comparatively lower absorption coefficient of the T2SL detectors presents a challenge, due to the trade-off (as a function of the absorber thickness) between large external quantum efficiency and higher collection efficiency/reduced dark current. This limitation can be addressed by incorporating thin detector absorber regions in resonant photonic architectures. One such architecture is the guided-mode resonance structure, comprising a high-refractive index grating layer sandwiched between two low-index layers[1]. Incident light diffracts into guided modes in the grating layer, which can then couple out to free space. When the outcoupled light interferes constructively/destructively with reflected/transmitted light, strong and narrow resonant peaks/dips can occur in the reflection/transmission spectra. We design a GMR structure where index-contrast required is achieved with highly doped (n**) which can be modeled with the Drude formalism, allowing for a lattice matched material system with extremely low semiconductor layers, refractive index in the MWIR, which can serve as a waveguide cladding layer. In this work, we build on our previous efforts[2], to demonstrate GMR-enhanced all-epitaxial uncooled (roomtemperature) MWIR nBn InAs/InAsSb T2SL detectors. We have designed, grown, fabricated and characterized GMR detectors showing such enhancement in a T2SL absorber only 250 nm thick. GaSb serves as a high-index grating layer which, together with the nBn detector (serving as a waveguide core), is sandwiched between a low-index n* virtual substrate and air. For grating periods A= 1.6 um and 1.8 um, resonances with enhancement of = 8x & 14 are shown at wavelengths, A= 4.4 um & 4.7 um respectively which is very close to the band-edge of the absorber (=5 um). Typically, due to the steep drop in absorption coefficient close to the band-edge, it is extremely difficult to obtain sufficient external quantum efficiency near the absorber band edge. Thus, detectors must be grown with lower energy cut-off, which will significantly increase dark current and degrade device detectivity. The ability to enhance EQE at the band edge of the absorber T2SL, allows us to use higher energy cut-off absorbers without degrading absorption efficiency. Moreover, the ultra-thin absorber, when compared to a typical MWIR detector, offers a significant reduction in dark current, when compared to traditional MWIR III-V detectors operating in same wavelength range, at similar temperatures. Significant improvement in both the optical and electrical performance of the GMR detectors results in superior specific detectivities. TE-polarized estimated specific detectivity D* = 1.2 x10 0 & 1 x19'0 cmvVHz/W are reported for the A= 1.6 um and 1.8 um devices, respectively. Future work will investigate polarization-independent detectors with substrate-side illumination for potential incorporation into focal-plane array architectures. The authors gratefully acknowledge United States Army under Prime Contract W9O09MY-20-P-0010 and National Science Foundation (ECCS-1926187 and ECCS-2025227). References: 1. S. S. Wang and R. Magnusson, Appl. Opt., vol. 32, no. 14, pp. 2606-2613, May 1993. 2. A. Kamboj, L. Nordin, P. Petluru, A. J. Muhowski, D. N. Woolf, and D. Wasserman, Appl. Phys. Lett., vol. 118, no. 20, p. 201102, 2021.

Guided-Mode Resonance Enhanced Room-Temperature Infrared Detectors

J: Novel Materials Epitaxy

technical paper

The Electronic Materials Conference (EMC) is the premier annual forum on the preparation, characterization and use of electronic materials. This year’s event will feature a plenary session, topical sessions, a poster session and more.

EMC is coordinated with the Device Research Conference (DRC). This recognizes the strong interaction between device and electronic materials research and provides fruitful exchange of information between attendees of both Conferences.

EMC 2023

The Electronic Materials Conference (EMC) is the premier annual forum on the preparation, characterization and use of electronic materials. 

R: Detectors and Narrow Bandgap Materials

After two years of virtual conferences, we're excited to host EMC 2022 in person at The Ohio State University in Columbus, Ohio. In addition to cutting-edge technical presentations given in multiple parallel sessions, opportunities to network with colleagues will be present throughout the conference. The size and format of the meeting makes networking easy, whether you have been coming to the conference for many years or are a first-time attendee.

EMC is coordinated with the Device Research Conference (DRC), which will be held the same week, from June 26-29. This recognizes the strong interaction between device and electronic materials research and provides fruitful exchange of information between attendees of both Conferences.

For information on the 80th Device Research Conference, please visit the DRC 2022 website.



EMC 2022

The Electronic Materials Conference (EMC) is the premier annual forum on the preparation, characterization and use of electronic materials. This year’s event will feature a plenary session, topical sessions, a poster session and more.

Leland Nordin

2

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Single-Phase Orthorhombic SnSe-PbSe Alloy Thin Films Stabilized on GaAs by Molecular Beam Epitaxy

Guided-Mode Resonance Enhanced Room-Temperature Infrared Detectors

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