Point and extended defects in heteroepitaxial β − G a 2 O 3 films

Wang

ACS Appl. Mater. Interfaces

et al. 2023

Incorporating emerging ultrawide bandgap semiconductors with a metal–semiconductor–metal (MSM) architecture is highly desired for deep-ultraviolet (DUV) photodetection. However, synthesis-induced defects in semiconductors complicate the rational design of MSM DUV photodetectors due to their dual role as carrier donors and trap centers, leading to a commonly observed trade-off between responsivity and response time. Here, we demonstrate a simultaneous improvement of these two parameters in ε-Ga2O3 MSM photodetectors by establishing a low-defect diffusion barrier for directional carrier transport. Specifically, using a micrometer thickness far exceeding its effective light absorption depth, the ε-Ga2O3 MSM photodetector achieves over 18-fold enhancement of responsivity and simultaneous reduction of the response time, which exhibits a state-of-the-art photo-to-dark current ratio near 108, a superior responsivity of >1300 A/W, an ultrahigh detectivity of >1016 Jones, and a decay time of 123 ms. Combined depth-profile spectroscopic and microscopic analysis reveals the existence of a broad defective region near the lattice-mismatched interface followed by a more defect-free dark region, while the latter one serves as a diffusion barrier to assist frontward carrier transport for substantially enhancing the photodetector performance. This work reveals the critical role of the semiconductor defect profile in tuning carrier transport for fabricating high-performance MSM DUV photodetectors.

Section: Resultsmentioning

confidence: 99%

Directional Carrier Transport in Micrometer-Thick Gallium Oxide Films for High-Performance Deep-Ultraviolet Photodetection

Wang

ACS Appl. Mater. Interfaces

et al. 2023

ACS Appl. Electron. Mater.

“…Finally, the bandgap can also decrease due to the presence of defects, which is the prevalent hypothesis in the literature. For example, in ref , it is found that defects in thin undoped β-Ga 2 O 3 films lower the observed optical bandgap from 4.85 to 4.57 eV. Using deep-level transient spectroscopy, this study shows several deep level states, ∼0.5–0.7 eV, below the conduction band.…”

Section: Resultsmentioning

confidence: 51%

“…Experimental VEELS bandgap values (black dots) vs theoretical bandgap from assuming defect states at the interface that lower the bandgap to 4.57 eV as measured in ref , exponentially decaying into β-Ga 2 O 3 with a decay length of 7 nm (red dashed line), convoluted with 15 nm Lorentzian broadening (red solid line).…”

Section: Resultsmentioning

confidence: 95%

“…Still, the assumption that we have a high concentration of vacancies that exponentially decline into the β-Ga 2 O 3 substrate could lead to the observed dip in the bandgap. To demonstrate that, we assume that the bandgap in the substrate next to the interface has the value of 4.57 eV measured in ref whereas the rate of increase is unknown. The electron probe typically has a delocalization effect of a few nanometers in VEELS.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Spatially Resolved Investigation of the Bandgap Variation across a β-(Al_xGa_1–x)₂O₃/β-Ga₂O₃ Interface by STEM–VEELS

Chmielewski

Deng

Moradifar

et al. 2022

Alloying β-(Al x Ga1–x )2O3 on a β-Ga2O3 substrate results in a heterojunction with a tunable bandgap, but is often plagued by defects in the interface region. In this work, using valence electron energy loss spectroscopy combined with density functional theory calculations, we identify a high concentration of cation interstitials at a β-(Al0.2Ga0.8)2O3/β-Ga2O3 interface and measure the optical absorption edge. We find a dip in the band edge of 0.1 eV depth and a width of around 15 nm on the β-Ga2O3 side of the interface with signs of noticeable electron probe delocalization broadening and discuss defect states versus excitons as its possible origins.

Physica Status Solidi (a)

“…The goal of this article is to explain the basics of TL, inform the reader about its capability as a great tool for measuring the energy levels of donors and acceptors in semiconductors, and bring the attention to the development of cryogenic thermally stimulated photoemission spectroscopy (C-TSPS) [55] which extends TL or thermally stimulated emission measurements to cover the entire range of shallow and deep levels in bandgap materials. Examples on successful applications of TL for the characterization of deep and shallow donors and acceptors in semiconductors [56][57][58][59][60] are discussed in detail revealing how this technique can be a powerful tool in the study of the electrical transport properties of semiconductors. Finally, the potential applications of C-TSPS in new research areas such as corrosion, radiation damage, ion implantation, and defects in oxides and other bandgap materials are discussed.…”

Section: Introductionmentioning

confidence: 99%

Advanced Thermoluminescence Spectroscopy as a Research Tool for Semiconductor and Photonic Materials: A Review and Perspective

Selim

2023

Self Cite

Thermoluminescence (TL) or thermally stimulated luminescence (TSL) spectroscopy is based on liberating charge carriers from traps in the bandgap by providing enough thermal energy to overcome the potential barrier of the traps. It provides a powerful tool to measure the positions of the localized states/traps in the bandgap. Despite that, its applications in semiconductors are very limited. Herein, the basics of TL spectroscopy and the recent advances in the technique with focus on cryogenic thermally stimulated photoemission spectroscopy (C‐TSPS) which extends TL measurements to cryogenic regime and allows the detection of very low concentrations of shallow and deep localized states is discussed. One goal herein is to introduce the reader to the use of TL and C‐TSPS in the characterization of semiconductors, explaining how it can be applied and demonstrating its advantages as a powerful tool for measuring shallow donor/acceptor ionization energies in semiconductors and as a method for characterizing compensating defects. The article also discusses interesting potential applications of C‐TSPS in new research areas such as corrosion and formation of oxide layers on metal surfaces.