[en] Knowledge about the temperature dependence of the fundamental band-gap energy of semiconductors is very important and constitutes the basis for developing semiconductor devices that work in a wide range of temperatures. Since the 90s, it has been suggested that III−V dilute bismides have temperature insensitive band gaps, and this fact might be important for semiconductor lasers, whose wavelength stays nearly constant through ambient temperature variations. Here, we have reviewed the available information about temperature evolution of the band gap for various III−V dilute bismide semiconductors. It is well known from many experimental results that the band-gap energy decreases monotonically with increasing temperature, and such behavior can be described by the Varshni formula. It is highly desirable for the Varshni temperature coefficient (α parameter) to be very small, indicating temperature insensitivity of the band gap. In this article, information about the band-gap temperature sensitivity or insensitivity is collected for chosen III−V bismides and discussed. (topical review)

[en] The temperature dependence of the band gap of GaN_xSb_1−x films with has been studied in the 1.1–3.3 m (0.35–1.1 eV) range using infrared absorption spectroscopy between 4.2 and 300 K. As with other dilute nitride semiconductors, the temperature dependence of the band gap is reduced by alloying with nitrogen when compared to the host binary compound. However, for GaNSb, the smallest variation of the band gap with temperature is observed for samples with the lowest N content for which the band gap is almost totally insensitive to temperature changes. This contrasts with the more widely studied GaN_xAs_1−x alloys in which the band gap variation with temperature decreases with increasing N content. The temperature-dependent absorption spectra are simulated within the so-called band anticrossing model of the interaction between the extended conduction band states of the GaSb and the localized states associated with the N atoms. The N next-nearest neighbor pair states are found to be responsible for the temperature insensitivity of the band gap of the GaNSb alloys as a result of their proximity to the conduction band edge giving them a more pronounced role than in GaNAs alloys. (paper)

[en] We have examined the alloy composition dependence of the energy bandgap and electronic states in GaAsNBi alloys. Using direct measurements of N and Bi mole fractions, via ion beam analysis, in conjunction with direct measurements of the out-of-plane misfit via x-ray rocking curves, we determine the “magic ratio” for lattice-matching of GaAsNBi alloys with GaAs substrates. Additionally, using a combination of photoreflectance and photoluminescence spectroscopy, we map the composition- and misfit-dependence of the energy bandgaps, along with revealing the energetic position of Bi-related states at approximately 0.18 eV above the valence band maximum.

[en] Photoreflectance (PR), photoluminescence (PL) and time-resolved PL were applied to study the optical properties, particularly the localized and delocalized states and carrier dynamics, in GaAs_1_−_xBi_x/GaAs quantum wells. With increasing Bi concentration the ground state transition (i.e., the transition between the first heavy hole and the first electron subband) red shifts due to Bi-related reduction of the GaAs_1_−_xBi_x energy gap. Additionally, the transition related to the excited states in the quantum wells is clearly observed for the sample with high Bi concentration of 5.6%, confirming these quantum wells are type I. The PL measurements show the S-shape behavior and indicate the strong localization effect below 150 K for all measured samples, while the PL emission above 150 K is related to delocalized states. The localized character of emission at low temperatures is confirmed by time-resolved PL studies. At 10 K the decay time has strong spectral dispersion (i.e. the decay time increases from ∼10 ns to ∼400 ns going from the high to low energy side of the PL peak). This dispersion disappears above 190 K. At room temperature the decay time is in the order of a few ns. (paper)

[en] In this work we present detailed studies of the influence of nitrogen and antimony on the optical quality of InNAs(Sb) alloys. We employed photoluminescence, photoreflectance and positron annihilation spectroscopy to reveal the role of antimony and nitrogen on the improvement/degradation of the optical qualities of InNAs(Sb) alloys. A series of 1 μm-thick InNAs(Sb) layers with different nitrogen and antimony concentrations were grown by molecular beam epitaxy. The results of these investigations show that Sb atoms serve as a surfactant which effectively improves the optical quality of InNAsSb alloys. The influence of nitrogen on the optical quality however is not the same as to what has been reported for other dilute nitrides. We observed an improvement of the optical quality for some nitrogen contents. These issues are comprehensively examined and explained. (paper)

[en] Optical properties and carrier dynamics in 6.6, 10.4, and 14.4 nm wide Ga(Sb, Bi)/GaSb quantum wells (QWs) with ∼10%–11% of Bi were studied by photoluminescence (PL), time-resolved PL, and transient reflectivity. Experiments revealed that low temperature emission is strongly governed by the decay of excitonic population that undergoes weak localization on the QW potential fluctuations rather than the strong defect-like localization typically found for highly mismatched alloys. This statement is supported first by the nearly linear increase of the PL intensity with the excitation power, second, by the lack of the S-shape signature in the temperature-dependent PL studies, and third, the absence of a strong lifetime dispersion for excitons. The low-temperature intraband carrier relaxation time is established in the range of 14–19 ps, nearly independent on the well width, while the exciton lifetime exhibits a well width dependence, i.e. this time decreases from ∼265 ps, through ∼206 ps, to ∼147 ps with the increase of the QW width from 6.6 to 14.4 nm. Our results demonstrate that in contrast to other dilute bismide alloys, GaSbBi behaves as a regular alloy rather than as a highly-mismatched material. (paper)

[en] Electron accumulation with a sheet density greater than 10¹³ cm⁻² usually occurs at InN surfaces. Here, the effects of treatment with ammonium sulfide ((NH₄)₂S_x) on the surface electronic properties of highly Mg-doped InN (>4×10¹⁸ cm⁻³) have been investigated with high resolution x-ray photoemission spectroscopy. The valence band photoemission spectra show that the surface Fermi level decreases by approximately 0.08 eV with (NH₄)₂S_x treatment, resulting in a decrease of the downward band bending and up to a 70% reduction in the surface electron sheet density

[en] Ga(In)SbBi alloys grown by molecular-beam epitaxy on GaSb substrates with up to 5.5% In and 1.8% Bi were studied by temperature- and power-dependent photoluminescence (PL) and compared to previous photoreflectance (PR) results. High energy and low energy PL peaks were observed and attributed respectively to Ga(In)SbBi bandgap-related emission and native acceptor-related emission. For GaSbBi below 100 K, the HE peak is at slightly lower energy than the bandgap determined from PR, indicating carrier localization. This phenomenon is significantly weaker in PL of GaInSbBi alloys, suggesting that the presence of indium improves the optical quality over that of GaSbBi. (paper)

[en] A study into the optimal deposition temperature for ultra-thin La₂O₃/Ge and Y₂O₃/Ge gate stacks has been conducted in this paper with the aim to tailor the interfacial layer for effective passivation of the Ge interface. A detailed comparison between the two lanthanide oxides (La₂O₃ and Y₂O₃) in terms of band line-up, interfacial features, and reactivity to Ge using medium energy ion scattering, vacuum ultra-violet variable angle spectroscopic ellipsometry (VUV-VASE), X-ray photoelectron spectroscopy, and X-ray diffraction is shown. La₂O₃ has been found to be more reactive to Ge than Y₂O₃, forming LaGeO_x and a Ge sub-oxide at the interface for all deposition temperature studied, in the range from 44 °C to 400 °C. In contrast, Y₂O₃/Ge deposited at 400 °C allows for an ultra-thin GeO₂ layer at the interface, which can be eliminated during annealing at temperatures higher than 525 °C leaving a pristine YGeO_x/Ge interface. The Y₂O₃/Ge gate stack deposited at lower temperature shows a sub-band gap absorption feature fitted to an Urbach tail of energy 1.1 eV. The latter correlates to a sub-stoichiometric germanium oxide layer at the interface. The optical band gap for the Y₂O₃/Ge stacks has been estimated to be 5.7 ± 0.1 eV from Tauc-Lorentz modelling of VUV-VASE experimental data. For the optimal deposition temperature (400 °C), the Y₂O₃/Ge stack exhibits a higher conduction band offset (>2.3 eV) than the La₂O₃/Ge (∼2 eV), has a larger band gap (by about 0.3 eV), a germanium sub-oxide free interface, and leakage current (∼10⁻⁷ A/cm² at 1 V) five orders of magnitude lower than the respective La₂O₃/Ge stack. Our study strongly points to the superiority of the Y₂O₃/Ge system for germanium interface engineering to achieve high performance Ge Complementary Metal Oxide Semiconductor technology

[en] The incorporation of Bi in GaSb_1_-_xBi_x alloys grown by molecular beam epitaxy is investigated as a function of Bi flux at fixed growth temperature (275 °C) and growth rate (1 μm h"-"1). The Bi content is found to vary proportionally with Bi flux with Bi contents, as measured by Rutherford backscattering, in the range 0 < x ≤ 4.5%. The GaSbBi samples grown at the lowest Bi fluxes have smooth surfaces free of metallic droplets. The higher Bi flux samples have surface Bi droplets. The room temperature band gap of the GaSbBi epitaxial layers determined from optical absorption decreases linearly with increasing Bi content with a reduction of ∼32 meV/%Bi