研究目的
To investigate the temperature dependence of the band gap in GaNxSb1-x alloys and understand the role of nitrogen pair states in inducing temperature insensitivity, contrasting with GaNAs alloys.
研究成果
The research demonstrates that GaNxSb1-x alloys exhibit significant temperature insensitivity in their band gap, particularly at low N contents, due to the influence of N next-nearest neighbor pair states located close to the conduction band edge. This is explained by a three-level BAC model, which accurately reproduces experimental data when including band gap renormalization and broadening effects. The findings contrast with GaNAs alloys, where temperature dependence decreases with increasing N content, highlighting the unique role of N pairs in GaNSb. This temperature insensitivity is beneficial for mid-infrared optoelectronic devices, and future studies could explore lower N contents or other material systems.
研究不足
The study is limited to GaNxSb1-x films with N content up to 1.3%, and samples with lower N content (below 0.18%) were not explored. The BAC models based on perturbation theory may not apply below certain thresholds, and the findings are specific to GaNSb alloys, with comparisons made primarily to GaNAs. Potential optimizations could include extending to lower N contents or other dilute nitride systems.
1：Experimental Design and Method Selection:
The study uses infrared absorption spectroscopy to measure the band gap temperature dependence in the 1.1–3.3 μm range (0.35–1.1 eV) from 4.2 to 300 K. The band anticrossing (BAC) model, specifically a three-level BAC model, is employed to simulate the interaction between GaSb conduction band states and localized N states, including isolated N and N pair states.
2：1–3 μm range (35–1 eV) from 2 to 300 K. The band anticrossing (BAC) model, specifically a three-level BAC model, is employed to simulate the interaction between GaSb conduction band states and localized N states, including isolated N and N pair states.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: Samples are 2 μm thick GaNxSb1-x films grown by plasma-assisted molecular beam epitaxy (MBE) on semi-insulating GaAs(001) substrates, with N contents ranging from 0.18% to 1.3%. A GaSb reference film is also used. N content is determined from high-resolution x-ray diffraction reciprocal space mapping.
3：18% to 3%. A GaSb reference film is also used. N content is determined from high-resolution x-ray diffraction reciprocal space mapping.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes a Panalytical XPert Pro MRD x-ray diffractometer with a 4-bounce Ge 220 Hybrid monochromator and triple-axis monochromator for Cu Kα1 radiation, a Bruker Vertex 70 V Fourier-transform infrared spectrometer (FTIR) with a liquid nitrogen-cooled HgCdTe detector (0.05–1.2 eV range), an Oxford Optistat CF-V continuous flow helium cryostat, and a gold mirror for reflection standards. Materials include GaNxSb1-x films and GaAs substrates.
4：05–2 eV range), an Oxford Optistat CF-V continuous flow helium cryostat, and a gold mirror for reflection standards. Materials include GaNxSb1-x films and GaAs substrates.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Films are grown by MBE with varying substrate temperatures. Reflectance and transmittance measurements are performed at 11° incidence angle with 1 meV resolution. Absorption coefficient is calculated from transmission and reflectance data. Hall effect measurements in Van der Pauw configuration determine carrier concentration and mobility at 295 K and 77 K.
5：Data Analysis Methods:
Absorption spectra are analyzed using linear extrapolation of α2 vs. hν curves for band gap determination. The three-level BAC model is used with parameters optimized to fit experimental data, including band gap renormalization and Gaussian broadening for electron-phonon interactions. Varshni and Bose-Einstein models are also referenced for temperature dependence parameterization.
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