Temperature Dependence Of Band Gap Research Articles

Analysis of the Photoluminescence Bandgap Temperature Dependence to Investigate the Doping of Micrometric Size GaAs Crystals Grown on Silicon for Tandem Solar Cells Applications

This work presents and discusses the extraction of the active dopants density of GaAs layers from the modeling of the bandgap temperature dependence derived from photoluminescence measurements.

Light Emission of Sn/Ge MQW pin Diodes on Si

Si-based photonic integrated circuits (PIC) with optically active components monolithically integrated on a Si chip are considered one of the solutions for the innovation of the next generation of information and communication technology. Si-based photonics opens up new possibilities for applications in data communications, sensor technology, biological and environmental sensing systems, but also future technologies including integrated quantum technologies, optical computing, artificial intelligence-based technologies and neuromorphic photonics. Remarkable advances have been made in key components of Si-based PICs, including high-performance Si-based modulators, photodetectors as well as waveguides. An efficient electrically pumped light source on Si still remains a challenge. The first lasers monolithically integrated on Si were demonstrated at low temperatures using the CMOS (Complementary Metal Oxide Semiconductor)-compatible material system SiGeSn.This paper reports the light emission from multiquantum well (MQW) structures composed of multi-stacked 2 Monolayer (ML) Sn/20 nm Ge layers incorporated into a pin structure. These samples were grown using molecular beam epitaxy. The schematic layer stack is shown in Figure (a). The MQW structure is placed in the intrinsic region of a Ge pin diode on a Si (100) substrate. Figure (b) shows the high-resolution x-ray (HR-XRD) space map of the device structure. The measurement data suggest that the compressively strained 2ML Sn/Ge MQW are grown pseudomorphically on the Ge virtual substrate (VS). Furthermore, the measurement shows clear information about the periodic Sn/Ge structure. In preliminary studies, the wetting layer thickness was determined to be 1.4 ML Sn. Figure (c) shows an atomic force microscopy (AFM) image of Sn dot formation on the Ge (100) surface for 2 ML Sn. The device is processed using a single mesa process with a very low thermal budget.The electroluminescence measurements are carried out in a cryostat, the temperature of which can be continuously regulated from room temperature (RT) to 12 K. The light is collected via a special indium fluoride multimode-fiber and detected with the NIRquest spectrometer in a wide wavelength range between 1000 nm and 2500 nm. In order to understand the influence of the MQW structure, a reference diode with exactly the same growth parameters but without Sn was grown and processed in parallel. Their temperature-dependent EL spectra are shown in figure (d). At RT we see the typical EL spectrum of a Ge diode with the direct band (Γ-HH) and indirect band (L-HH) transition. Due to the indirect semiconductor properties of Ge, the intensity decreases with lower temperatures. The maxima shift towards the blue because of the temperature dependent band gap. At very low temperatures a new luminescence occurs, which we identify as a defect luminescence of the Ge.The temperature-dependent EL spectra of the 2 ML/Ge MQW pin diode are shown in figure (e). Four peaks can be observed depending on the temperature. At RT the Ge peak as in the reference sample can be measured, but with a different intensity ratio. At very low temperatures we find a second, sharper peak next to the defect luminescence peak of Ge (see inset). This shows a direct behavior because the EL intensity increases with decreasing temperature. In the paper we discuss these different peaks in detail and give an interpretation based on photogenerated carrier numbers, temperature dependent occupation and quantum confined radiative transmission probabilities. Figure 1

High-temperature transport properties of a two-dimensional weakly doped parabolic semiconductor

A version of the Mexican-hat Hamiltonian is used to study high-temperature transport properties of a two-dimensional weakly doped semiconductor with electron-hole symmetric bands. For a finite doping level and a temperature-dependent band gap, we find a closed analytical form of the temperature-dependent chemical potential. The effective concentrations of charge carriers participating in transport coefficients are analyzed in the space spanned by the total electron concentration and temperature. It is shown that these concentrations are the sum of a residual contribution and two thermally activated contributions, with a complicated dependence on temperature. The analytical expression for the Hall coefficient RHis also found. It is argued that it is a non-monotonic function of the doping level with the maximum at the doping nmax that is a linear function of temperature at high enough temperatures. The analysis of the real part of the interband conductivity shows that it is inversely proportional to incoming photon energy at low temperatures and that it is nearly constant over a wide energy range at high temperatures. This results are expected to be of significant importance in understanding transport and optical properties of weakly doped two-dimensional semiconductors with nearly symmetric parabolic bands.&#xD.

Exploring Temperature-Dependent bandgap and Urbach energies in CdTe thin films for optoelectronic applications

This study examines CdTe thin films deposited via RF magnetron sputtering, focusing on structural and optical properties. X-ray diffraction, Raman spectroscopy, and SEM assessed structural characteristics. Optical properties were analyzed through transmittance measurements from 10 to 300 K. Tauc plots and Varshni modeling revealed a temperature-dependent bandgap, increasing from 1.49 eV at room temperature to 1.57 eV at 10 K. Urbach energy rose from 82.7 to 93.7 meV with temperature. These results are essential for applications where temperature affects CdTe-based device performance.

Contribution of individual phonon to the band gap renormalization in semiconductors

Understanding the origin of temperature-dependent bandgap in semiconductors is essential for their applications in photovoltaics, optoelectronic and space applications. In this regard the electron–phonon coupling is known to play a crucial role in the temperature dependence of the bandgap of semiconductors. Several models have also been proposed in this regard which are also found experimentally compatible; however, these models need to account for more information about the contribution of individual modes in band gap renormalization. The present report is an analytical attempt to do so by utilizing the Bose–Einstein oscillator model, thereby discussing a method for finding the individual renormalization term contributed by respective phonon modes to the overall bandgap. This study contributes to the fundamental understanding of the temperature variation of optical properties of semiconductors that correlates with the role of electron–phonon interaction.

Temperature-dependent optical bandgap of TiO2 under the Anatase and Rutile phases

A crucial step in developing new and/or more efficient devices relies on the detailed knowledge of the properties of their main (elemental or combined) parts. The same applies to titanium dioxide TiO2 that forms the basis of today numerous applications whose performances are determined by the presence or relative amount of the Anatase (A-) and Rutile (R-) most common phases of TiO2. Whereas the basic structural characteristics of these two polymorphs are very well-established, some of their optical aspects still deserve attention. With these ideas in mind this work presents a comprehensive investigation of the optical bandgap Egap of TiO2 under the Anatase and Rutile phases. The study considered pure A-TiO2 and R-TiO2 samples in the form of powder, and optical reflectance and Raman spectroscopy in the 83–823 K temperature range. In addition to reliable Egap values the study explores their temperature-dependent Egap(T) behavior that is expected to assist future advancements in the field of TiO2-based materials and devices (thin films, interfaces, low-dimensional systems, and photocatalytic and solar cells, for example).

Influence of temperature on bandgap shifts, optical properties and photovoltaic parameters of GaAs/AlAs and GaAs/AlSb p–n heterojunctions: insights from ab-initio DFT + NEGF studies

The III–V group semiconductors are highly promising absorbers for heterojunctions based solar cell devices due to their high conversion efficiency. In this work, we explore the solar cell properties and the role of electron–phonon coupling (EPC) on the solar cell parameters of GaAs/AlSb and GaAs/AlAs p–n heterojunctions using non-equilibrium Green function method (NEGF) in combination of ab-initio density functional theory (DFT). In addition, the band offsets at the heterointerfaces, optical absorption and bandgap shifts (BGSs) due to temperature are estimated using DFT + NEGF approach. The interface band gaps in heterostructures are found to be lower than bulk band gaps leading to a shift in optical absorption coefficient towards lower energy side that results in stronger photocurrent. The temperature dependent electronic BGS is significantly influenced by the phonon density and phonon energy via EPC. The phonon influenced BGS is found to change the optical absorption, photocurrent density and open-circuit voltage. In case of GaAs/AlSb junction, the interface phonons are found to have significantly higher energies as compared to the bulk phonons and thereby may have important implications for photovoltaic (PV) properties. Overall, the present study reveals the influence of EPC on the optical absorption and PV properties of GaAs/AlSb and GaAs/AlSb p–n heterojunctions. Furthermore, the study shows that the DFT + NEGF method can be successfully used to obtain the reasonable quantitative estimates of temperature dependent BGSs, optical absorption and PV properties of p–n heterojunctions.

Dielectric, electrical and optical properties of a Ni-substituted double perovskite ceramic

In this report, iron based double perovskite oxide Ca2Fe0.85Ni0.15NbO6 was successfully synthesized adopting the solid state reaction method. The structure and microstructure along with the purity, frequency and temperature dependent dielectric properties, energy storage and band gap modulation properties of the ceramic is also discussed. The ceramic shows a small band gap with a high remnant polarization which aligns it toward ferroelectric photovoltaic device applications. The temperature stable dielectric constant of the material up to a high temperature range is useful for MLCC applications. The energy storage density of the material is calculated from room temperature hysteresis loop. The frequency variation of ac conductivity refers Jonscher’s law. The temperature variation of frequency exponent term n indicates CBH (correlated barrier hopping), model of the conduction mechanism in the sample. The presence of room temperature M-H loop with negligible magnetization and coercive value indicates the soft ferromagnetic behavior of the ceramic.

Ab initio study of temperature-dependent piezoelectric and electronic properties of thermally stable GaPO4.

Gallium-phosphate (GaPO4) is one of the ultra-high thermally stable piezoelectric materials with a high critical temperature of 1206 K. Here, first principles calculations with quasi-harmonic approximation are performed to study thermal and other physical properties of α-GaPO4. For the electronic structure, we focus on the electron-phonon interaction and lattice expansion effects on the temperature-dependent band gap, which plays a significant role in zero-point renormalization. Significantly, the large piezoelectric constants e11 primarily comes from intrinsic sensitivity of Ga and O sites to axial strain, while P atoms contribute little, which remains true in other quartz-like type APO4 (A = B, Al, In). Our work provides an insight into the temperature-dependent electronic and piezoelectric properties of α-GaPO4 and motivates its applications in a high temperature environment.

High-performance CsSnBr<sub>3</sub>/Si PN heterojunction photodetectors prepared by pulsed laser deposition epitaxy

Halide perovskite semiconductors have outstanding physical properties such as high light absorption coefficient, large carrier diffusion length, and high photoluminescence quantum efficiency, and demonstrate significant potential applications in optoelectronic devices such as photodetectors and solar cells. However, the toxicity and environmental instability associated with lead-based perovskites significantly limit their applications. An attractive solution is substituting tin for lead in perovskites and growing high-quality tin-based perovskite films. In this study, we adopt the pulsed laser deposition method to achieve the epitaxial growth of CsSnBr<sub>3</sub> films on silicon substrates. The morphologies, optical and electrical properties of the CsSnBr<sub>3</sub> films, as well as the CsSnBr<sub>3</sub>/Si heterojunction detectors, are comprehensively investigated with various characterization techniques, including XRD 2<i>θ</i>-<i>ω</i> and <i>φ</i> scans, atomic force microscope, scanning electron microscope, photoluminescence and time-resolved photoluminescence spectroscopy, and Hall electrical measurements. The results indicate that such a CsSnBr<sub>3</sub> film grows epitaxially onto the silicon substrate via a face-to-face mode. Interestingly, an unusual temperature-dependent bandgap increase is found to be due to the high electron effective mass of CsSnBr<sub>3</sub>. The CsSnBr<sub>3</sub> film shows the P-type semiconductor behavior with a high mobility of 122 cm²/(V·s), enabling the formation of an ideal Type-II heterojunction with the silicon substrate. The CsSnBr<sub>3</sub>/Si semiconductor heterojunction detector exhibits distinctive heterojunction PN diode characteristics in the dark and a pronounced photoresponse under illumination. At zero bias, the detector displays a switch ratio exceeding 10<sup>4</sup>, responsivity of 0.125 mA/W, external quantum efficiency of 0.0238%, detectivity (<inline-formula><tex-math id="Z-20240301150440">\begin{document}$D^* $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231645_Z-20240301150440.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231645_Z-20240301150440.png"/></alternatives></inline-formula>) of 2.1×10<sup>9</sup> Jones, response time 3.23 ms, and recovery time of 4.87 ms. Under a small bias of –1 V, the switch ratio decreases to 50, but responsivity and external quantum efficiency increase by 568 times. The detectors can maintain self-powered operation state with a high switch ratio of 10<sup>4</sup>, millisecond-level response time and millisecond-level recovery time. In conclusion, this work presents a self-powering, high-performance photodetector based on CsSnBr<sub>3</sub> epitaxial films integrated with silicon substrates.

Cu2ZnGeSe4 single crystals: Growth, structure and temperature dependence of band gap

This work describes the production of single crystals of the semiconducting quaternary compound Cu2ZnGeSe4 using a gas chemical method in which iodine was used as a transporter. For all the synthesized samples, their phase state, crystal structure syngony and lattice constants were refined. The unit cell of the studied compound is characterized by tetragonal symmetry. The transmission spectrum was applied to calculate the band gap, which is depicted as temperature function in 20–300 K range. It was fixed that the band gap increases by 12% with decreasing temperature.

Studies on temperature-dependent bandgap and gap-to-midgap ratio in diamond lattice photonic crystal with biosensing applications

The present study examines the temperature dependence of the photonic bandgap, the corresponding wavelength and the gap-to-midgap ratio in a three-dimensional diamond lattice photonic crystal. The bandgap calculations establish that the structure shows a complete photonic bandgap centered around 1550 nm at 300 K. The thermo-optic effect, observed in silicon, is employed to compute the photonic bandgap, band-edge wavelengths and mid-bandgap wavelength at various temperatures in the range of 300 K–400 K. The gap-to-midgap ratio, for the proposed structure, is also evaluated at different temperatures. It is seen that the upper and lower band-edge wavelengths and the mid-bandgap wavelength show a linear temperature dependence. The sensitivity of the structure is observed to be 0.0518 nm/K, thus supporting temperature sensing applications. It is found that the gap-to-midgap ratio, for the proposed diamond lattice structure, shows linear variation with temperature. The effect of variation of the dielectric constant and the fill factor on the gap-to-midgap ratio for the diamond structure has also been analyzed. The proposed design has also been analyzed as a refractive index sensor with a sensitivity of 254.9 nm/RIU for sensing the different components of blood.

Optical, structural and dielectric properties of solvothermally grown molybdenum sulfide nanosheets

MoS2 nanosheets have been synthesized by simple and conventional solvothermal methods. FEG-TEM images reveal that the produced MoS2 sample has a hexagonal crystal structure with large (2μm) nanosheets. The XRD and Raman spectra of the samples also confirm the hexagonal crystal phase. The schematic refined unit cell with electron density mapping is visualized after Rietveld refinement. The optical properties such as absorbance, PL, refractive index, extinction coefficient, dielectric constant, optical conductivity, etc. have been investigated in the wavelength range of 330nm to 1000nm. The normal dispersion (ND) and the anomalous dispersion (AD) regions have been observed in the refractive index spectrum. The estimated carrier concentration has been found to be 5×104cm−3. The temperature-dependent indirect bandgap of MoS2 has been simulated using a semi-empirical formula based on electron-phonon coupling and it decreases with increasing temperature. The calculated average lifetime of carriers is 1.17 ns. The grown MoS2 shows large dielectric constant and low tangent loss in the frequency range of 5–500 kHz. The Nyquist plot of the sample gives the NTCR (negative temperature coefficient of resistance) behaviour like a semiconductor. The activation energy (EA) has been estimated from temperature dependence AC conductivity.

Understanding the temperature sensitivity of the photovoltaic parameters of perovskite solar cells

Perovskite solar cells (PSCs) have promised high-efficiency and low-cost solar-to-electrical conversion that now go outdoors for practical applications; however, the elevated outdoor temperature remarkably affects the photovoltaic efficiency. To date, there has been little work about understanding the temperature sensitivity of PSCs. Here, we build an analytical model to understand the temperature sensitivity and the limiting factors of temperature coefficient (TC) in PSCs. Our model is based on diffusion-drift numerical method by involving the temperature-dependent bandgap and band edge of perovskite layers, which quantitively describe the effect of many physical factors, including carrier recombination channels, trap density, band alignment and band variation of transport layers. It was found that the built-in electrical field and minority carrier concentration at interface are closely corrected with temperature, that is responsible for the temperature sensitivity of device performance. We show that this model can be used to explain the disparate temperature sensitivity of a series of reported real PSCs, and also gives potential pathways for the design and fabrication of temperature-insensitive photovoltaics towards practical applications.

Temperature dependence of band gap of CeO2 nanoparticle photocatalysts

Temperature dependence of band gap of CeO2 nanoparticle photocatalysts

Nonmonotonic temperature-dependent bandgap change of CsPbCl3 films induced by optical phonon scattering

The CsPbCl3 perovskite films are successfully grown on quartz substrates by radio frequency (RF)-magnetron sputtering method and their detailed photoluminescence properties are studied over the temperatures from 10 K to 300 K. There exists one near bandgap emission peak (∼410 nm) in the violet region with typical lifetime of few nanoseconds at room temperature. To our surprise, with temperature increasing, this band shows nonmonotonic shift, which is different to the traditional semiconductor like silicon or the same group of perovskites like MAPbI3 or CsPbBr3. The origin of this band and its temperature-dependent shift can be well described with the Bose-Einstein two-oscillator model that takes into account the interaction between electrons and phonons including acoustic phonons and optical phonons. Due to the anisotropic optical properties of the perovskite crystal, the (001)-orientated films have stronger electron phonon coupling and weaker exciton binding energy.

Effect of spin-orbit coupling on the zero-point renormalization of the electronic band gap in cubic materials: First-principles calculations and generalized Fröhlich model

The electronic structure of semiconductors and insulators is affected by ionic motion through electron-phonon interaction, yielding temperature-dependent band gap energies and zero-point renormalization (ZPR) at absolute zero temperature. For polar materials, the most significant contribution to the band gap ZPR can be understood in terms of the Fr\"ohlich model, which focuses on the nonadiabatic interaction between an electron and the macroscopic electrical polarization created by a long-wavelength optical longitudinal phonon mode. On the other hand, spin-orbit interaction (SOC) modifies the bare electronic structure, which will, in turn, affect the electron-phonon interaction and the ZPR. We present a comparative investigation of the effect of SOC on the band gap ZPR of twenty semiconductors and insulators with cubic symmetry using first-principles calculations. We observe a SOC-induced decrease of the ZPR, up to 30%, driven by the valence band edge, which almost entirely originates from the modification of the bare electronic eigenenergies and the decrease of the hole effective masses near the $\mathrm{\ensuremath{\Gamma}}$ point. We also incorporate SOC into a generalized Fr\"ohlich model, addressing the Dresselhaus splitting which occurs in noncentrosymmetric materials, and confirm that the predominance of nonadiabatic effects on the band gap ZPR of polar materials is unchanged when including SOC. Our generalized Fr\"ohlich model with SOC provides a reliable estimate of the SOC-induced decrease of the polaron formation energy obtained from first principles and brings to light some fundamental subtleties in the numerical evaluation of the effective masses with SOC for noncentrosymmetric materials. We finally warn about a possible breakdown of the parabolic approximation, one of the most fundamental assumptions of the Fr\"ohlich model, within the physically relevant energy range of the Fr\"ohlich interaction for materials with high phonon frequencies treated with SOC.

Temperature dependence of the band gap of Si28 :P at very low temperatures measured via time-resolved optical spectroscopy

We measure the temperature dependence of the indirect band gap of isotopically purified $^{28}\mathrm{Si}$:P in the regime from 0.1 K to 3 K by high-resolution absorption spectroscopy of the donor bound exciton transition. The measurements increase the up-to-date precision of the temperature-dependent band gap change by more than one order of magnitude and reveal a ${\mathrm{T}}^{4}$ dependence which is about a factor of two less than observed in previous measurements. Such a ${\mathrm{T}}^{4}$ dependence is predicted by theory, but the absolute values differ between our experiment and the most up-to-date calculations by a factor of 30, corroborating that the electron-phonon interaction at low temperatures is still not correctly included into theory. What is more, the ability of such very high-precision band-gap measurements facilitates the use of time- and spatially resolved $^{28}\mathrm{Si}$:P absorption as a contactless, local thermometer and electric field sensor with a demonstrated time resolution of milliseconds.

Optical properties of AgxCu1–xI alloy thin films

We report on the excitonic transition energy E0 and spin–orbit split-off energy Δ0 of γ-AgxCu1–xI alloy thin films studied by using reflectivity measurements at temperatures between 20 K and 290 K. The observed bowing behavior of the E0 transition as a function of the alloy composition is explained based on first-principles band structure calculations in terms of different physical and chemical contributions within the description of ordered alloys. The spin–orbit coupling is found to increase from a value of 640 meV for CuI to approximately 790 meV for AgI. Furthermore, we show that the temperature-dependent bandgap shift between 20 K and 290 K decreases with increasing Ag-content from 25 meV for CuI to 6 meV for AgI. We attribute this behavior mostly to changes in the contribution of thermal lattice expansion to the bandgap shift.

Temperature dependence of the energy band gap in ZrTe5 : Implications for the topological phase

Using Landau level spectroscopy, we determine the temperature dependence of the energy band gap in zirconium pentatelluride (ZrTe$_5$). We find that the band gap reaches $E_g=(5 \pm 1)$ meV at low temperatures and increases monotonously when the temperature is raised. This implies that ZrTe$_5$ is a weak topological insulator, with non-inverted ordering of electronic bands in the center of the Brillouin zone. Our magneto-transport experiments performed in parallel show that the resistivity anomaly in ZrTe$_5$ is not connected with the temperature dependence of the band gap.