Temperature effects in silicon solar cells

The temperature variation of the relative spectral response RSR, short circuit current I_sc and open circuit voltage V_oc is measured and the results are theoretically discussed. The RSR at wavelengths larger than the peak wavelengths always increases with temperature. The observed increase is found to agree with theory when temperature variation of the absorption coefficient of light and of L_n the carrier diffusion length in the base is taken into account properly. The temperature variation of short wavelength RSR depends on S, the surface recombination velocity and $\text{L}{}_{\mathrm{p}}\text{d}\text{, L}{}_{\mathrm{p}}$ is the carrier diffusion length in the diffused layer and d is the junction depth. If S is small and $\text{L}{}_{\mathrm{p}}\text{d}$ is large, the RSR is practically independent of temperature. On the other hand if S is large and/or $\text{L}{}_{\mathrm{p}}\text{d}$ is small, the RSR decreases as the temperature increases.A new relation between L_n, d and the peak position of RSR is derived. The observed temperature shift in the peak position agrees well with that predicted by this relation.The temperature increase of I_sc and decrease of V_oc are different for AM0 and AM1 illuminations. The observed differences can be explained at least qualitatively on the basis of the results obtained in this paper.     

Structural disordering and viedemann-franz relation in melts of some II-IV-V<Subscript>2</Subscript> semiconductors

The thermal and electrical conductivities, as well as the thermoelectric power of the CdSnAs₂, CdGeAs₂, ZnSnAs₂, and ZnGeAs₂ ternary semiconductor compounds, were studied in both solid and liquid states. It was shown that the thermal and electrical conductivities of these compounds increase, while the thermoelectric power decreases in the course of melting to the values characteristic of liquid metals. In contrast to metal melts, the electrical conductivity and the Lorentz numbers calculated from the Viedemann-Franz relation increase with temperature in II-IV-V₂ semiconductor melts. According to the Mott classification, the melts of these compounds are related to group B. Melting of II-IV-V₂ semiconductors causes their metallization.     

Reduction of the anomalous VT behavior in MOSFETs with high-κ/metal gate stacks

This study investigates the impact of different nitridation processes on hafnium silicon oxynitride (HfSiON) dielectrics. It is demonstrated that the threshold voltage (V_T vs. L_g) behavior at short gate lengths is strongly impacted by the nitridation process, depending on the Hf/(Hf+Si) ratio and the HfSiON thickness. A Plasma nitridation in oxidizing ambient results in a modification of the dielectric that can explain the anomalous V_T behavior in devices integrated with hafnium-based dielectrics and metal gate. Reduction in anomalous V_T behavior and limited gate leakage is achieved by applying a thermal nitridation in a NH₃ ambient on Hf-rich silicon oxynitride.     

On the band gap and thermal expansion of MnIn5.0S8.5 single crystals

MnIn_5.0S_8.5 single crystals are grown by the Bridgman method. The width and length of the crystals are ～14 and ～40 mm, respectively. The composition, structure and unit-cell parameter of the crystals are established. From the transmittance spectra recorded in the temperature range 20–300 K, the band gap E _g and its temperature dependence E _g (T) are determined. The dependence E _g (T) is adequately described by the corresponding theoretical expression. The specific expansion (Δl/l ₀) versus temperature is measured, and the coefficient of linear thermal expansion (α _L ) is determined. From the data on α _L , the Debye temperature (Θ_D) and the rms dynamic atomic displacements \((\sqrt {\bar u^2 } )\) are calculated. It is established that the Debye temperature Θ_D decreases with increasing temperature, whereas the rms atomic displacements increase.     

High electric field effects in amorphous semiconducting (As2S3)1−x(PbS)x

High electric field measurements on (As₂S₃)_1?x(PbS)_x amorphous semiconductors have been made in sandwich geometry at 50 and 80°C. They reveal the non-linear effects associated with conduction in amorphous semiconductors. The x = 0.1 composition exhibits an anomalous increase in current at an applied field of about 22.5 KV/cm which is found to be independent of the temperature.     

Static and low-frequency noise characterization in submicron MOSFETs for memories cells applications

In this paper, we present the extraction of oxide traps properties of n-metal-oxide-semiconductor (N-MOS) field effect transistors with W×L=0.5×0.1 μm² using low-frequency (LF and random telegraph signal) noise and static I(V) characterizations. The impact of oxide thickness, on static and noise parameters is analyzed. Static measurements on N-MOS devices with different tunnel oxide thickness show anomalies (a significant increase in V_t values for low temperature and kink effect) attributed to traps located in the oxide. From LF noise analysis we find that 1/f noise stems from carrier number fluctuations. The slow oxide trap concentration deduced from the noise data is about 10¹⁵ eV/cm³ in agreement with the state-of-the-art gate oxides. Finally, drain current RTS amplitude as large as 10% have been observed.     

Thermal expansion and characteristic features of the strength of interatomic bonds in melts of III–V compounds (AlSb, GaSb, InSb, GaAs, InAs)

The temperature dependence of the specific volume of melts of III–V compounds has been studied thermometrically and with penetrating γ radiation. The thermal expansion of these melts has been estimated at various temperatures. Based on the similarity of the structure of the melts and the elastic continuum, the characteristic Debye temperatures and rms dynamic displacements of the atoms in the close-range-order structure of these melts have been calculated from the estimated thermal expansion. A considerable change in the indicated characteristics is observed at the transition from the solid state to the liquid state, indicating significant changes in the vibrational spectrum of III–V compounds upon melting. The thermal expansion of the melts is observed to increase upon heating, indicating a further loss of strength of the interatomic bonds in the melts with growth of temperature. Fiz. Tekh. Poluprovodn. 32, 429–431 (April 1998)     

Luminescent properties of BexCd1−xSe thin films

We report photoluminescence (PL) study of Be_xCd_1−xSe epitaxial layers (x<0.21) grown by molecular beam epitaxy on InP substrates. Continuous wave PL spectra are taken within a 4.2-300 K temperature range. We observe an anomalous ‘s-shaped’ temperature dependence of emission energy and a severe decrease of emission intensity with the increase of temperature. We explain an ‘s-shaped’ temperature dependence of emission energy by exciton localization in the potential minima at low temperatures followed by thermal activation at higher temperatures. We attribute low emission intensity at high temperatures to exciton dissociation and electron/hole migration to non-radiative recombination centers.     

New insight on negative bias temperature instability degradation with drain bias of 28 nm High-K Metal Gate p-MOSFET devices

The degradation of negative bias temperature instability (NBTI) on 28 nm High-K Metal Gate (HKMG) p-MOSFET devices under non-uniform stress condition has been systematically studied. We found the asymmetry between forward and reverse Idsat shift under non-uniform stress condition is significant for long channel devices even under low drain bias stress (e.g., Vds = −0.1 V and gate channel length L = 1 μm), and seems to be dominated by a minimally required critical length (L = 0.2 μm derived from the experimental data). To the authors’ best knowledge, these are new phenomena reported. We attribute these anomalous NBTI characteristics with drain bias to the local self-heating (LSH) activated NBTI degradation mechanism. One semi-empirical analytical model, which fits well with our experimental data, is then proposed in this paper.     

Electron bombardment effect on the reverse I–V characteristics and tensosensibility of p+-nGaAs diodes

The effect of ≈2 MeV electron bombardment on the reverse characteristics and tensoelectric properties in p⁺-nGaAs diodes is investigated. The reverse breakdown voltage showed a weak increase due to irradiation and an anomalous temperature dependence in the range 77–300 K. The I–V characteristics in electron-irradiated diodes revealed a high pressure sensitivity (tensosensibility) to the external hydrostatic pressure (up to 6 · 10⁸ Pa). The peculiarities in the reverse I–V characteristics of diodes investigated point to the presence of a radiation-induced deep trap (acceptor-type level at about E₀ ? 0.3 + 0.4 eV), which is attached to the Γ₁₅^V-maximum of the valence band.     

Nature of the diamagnetic maximum in the temperature dependences of the magnetic susceptibility of crystals of (Bi2 ? x Sb x )Te3 alloys (0 < x < 1)

The temperature dependences of the magnetic susceptibility ?? of crystals of (Bi_{2 ? x} Sb _x )Te₃ alloys (0 < x < 1) are studied using a SQUID magnetometer in the temperature range from 2 to 400 K with the parallel and perpendicular orientations of the vector of magnetic field strength H relative to the trigonal axis of the crystal C ₃ (H ?? C ₃ and H ?? C ₃). It is found that the diamagnetic susceptibility of the samples with x = 0.2 (Bi_1.8Sb_0.2Te₃) and x = 0.5 (Bi_1.5Sb_0.5Te₃) increases in the range from 50 K to temperatures preceding the emergence of intrinsic conductivity (250 K). It is found that the diamagnetic maximum manifests itself in the same temperature range, in which an anomalous increase in the Hall coefficient is observed. It is shown that the nature of the diamagnetic maximum is associated with the nonparabolicity of the energy spectrum of light diamagnetic holes, a decrease in whose concentration is accompanied by a decrease in their effective masses, which provides an increase in the diamagnetic susceptibility with increasing temperature. These results are confirmed by the dynamics of the temperature variation in the resonance frequency of plasma oscillations of free charge carriers.     

Stressing organic light-emitting diode under constant-brightness driving mode

The degradation of the organic light-emitting diodes (OLEDs) was studied under the constant-brightness driving mode. The time-dependent current exhibits a long period of linear increase followed by an exponential increase before the eventually catastrophic failure featured by a vertical increase. A new lifetime T_th is defined as the time for the device to reach the end of the linear increase stage. Similar to the well-known relation between the lifetime and the brightness in the constant-current driving mode, the lifetime and the brightness in the constant-brightness driving mode also fit the formula Lⁿ × T_th = Const., where L is the brightness and n is the acceleration exponent. By examining the current density–voltage–luminance characteristics and the photoluminescence intensity of the devices before and after the stress, it is found that both the reduction of the charge injection efficiency, and the loss of the emissive centers, contribute to the OLEDs’ degradation. The extra power supplied to the device to keep the brightness constant, raises the junction temperature, and eventually leads to the catastrophic failure of the devices.     

Ferromagnetism and anomalous transport in GaAs doped by implantation of Mn and Mg ions

GaAs layers doped by implantation of Mn and Mg ions to increase the hole concentration were synthesized and studied. Measurements using a SQUID magnetometer showed that there is ferromagnetism at temperatures as high as 400 K, which is related to the formation of the MnAs and Mn _y Ga_{1 ? y} clusters as a result of high-temperature annealing, in addition to the formation of the Ga_{1 ? x} Mn _x As alloy. The anomalous Hall effect was observed at temperatures in the range from 4.2 to 200 K. As temperature was increased starting with 4.2 K, the negative magnetoresistance with extremely large magnitude transformed into a giant positive magnetoresistance at T ≈ 35 K.     

Effect of temperature and rare-earth doping on charge-carrier mobility in indium-monoselenide crystals

In the temperature range T = 77-600 K, the dependence of the charge-carrier mobility (μ) on the initial dark resistivity is experimentally investigated at 77 K (ρd ₀), as well as on the temperature and the level (N) of rare-earth doping with such elements as gadolinium (Gd), holmium (Ho), and dysprosium (Dy) in n-type indium-monoselenide (InSe) crystals. It is established that the anomalous behavior of the dependences μ(T), μ(ρd ₀), and μ(N) found from the viewpoint of the theory of charge-carrier mobility in crystalline semiconductors is related, first of all, to partial disorder in indium-monoselenide crystals and can be attributed to the presence of random drift barriers in the free energy bands.     

High-temperature ferromagnetism of Si1 ? x Mn x films fabricated by laser deposition using the droplet velocity separation technique

The transport and magnetic properties of Si_{1 ? x} Mn _x films of thickness 55?C70 nm with various Mn content (x = 0.44?C0.6) are studied in the temperature range of 5?C400 K and in magnetic fields up to 2 T. The films are grown by pulsed laser deposition on Al₂O₃ (0001) substrates at a temperature of 340°C using velocity separation of deposited particles. The films exhibit metal conductivity and the resistivity ?? = (2?8) × 10^?4 ?? cm, typical of highly degenerate semiconductors. It is found that the anomalous component of the Hall effect dominates over the normal component at T = 300 K for the Si_{1 ? x} Mn _x alloy with x ?? 0.5, and that the Curie temperature significantly exceeds room temperature and is estimated as ??500 K from magnetization measurements (for MnSi silicide the Curie temperature is T _C = 30 K). It is shown that the anomalous component of the Hall conductivity at low temperatures is controlled by ??side-jump?? and (or) ??intrinsic?? mechanisms independent on the carrier scattering time. The results are explained by features of the formation of defects with localized magnetic moments in the case of Si_{1 ? x} Mn _x films with x ?? 0.5 and by the significant role of matrix spin fluctuations in the exchange between these defects.     

Determination of the diffusion length of minority charge carriers in a semiconductor from the dynamic nonequilibrium I–V characteristics of MIS structures

A method for determination of the diffusion length L _de of minority charge carriers in a semiconductor from the dynamic nonequilibrium I–V characteristics of metal-insulator-semiconductor (MIS) structures is proposed. The method makes it possible to exclude the effect of bulk generation in a semiconductor on L _de and decrease the temperature of measurements. The possibility of investigating the effective L _de profile in the semiconductor surface layer is shown for the case of nonuniform depth distribution of electrically active defects in a material. The values of L _de in MIS structures on silicon used in integrated-circuit technology are investigated. The effect of the internal gettering of defects in silicon and the irradiation of MIS structures by low-energy electrons (10–30 keV) on the effective L _de profiles in the surface layer of a semiconductor is considered.     

Voltage dependent degradation of HfSiON/SiO2 nMOSFETs under positive bias temperature instability

This paper investigates voltage-dependent degradation of HfSiON/SiO₂ nMOSFETs under conditions of positive bias temperature instability (PBTI), and proposes a PBTI degradation model that can use data from acceleration tests to predict device lifetime accurately. Experimental results show that the PBTI stress generated shallow traps in HfSiON and the exponent of power-law for threshold-voltage shift increased exponentially with an increase of PBTI stress voltage. An enhancement factor that represents creation of shallow charge traps in gate dielectric by PBTI stress was included in the proposed model. The proposed model predicted operational lifetime t_L = 1.64 × 10¹⁰ s, which agreed well with the t_L = 1.92 × 10¹⁰ s measured at low gate stress voltage, whereas the conventional model overestimates t_L by an order of magnitude, demonstrating that the proposed model is very useful on shortening the measurement time for estimating t_L of high-k nMOSFETs.     

Lorentz number and Hall factor in degenerate semiconductors during resonance scattering of charge carriers

In highly degenerate semiconductors, the Lorentz number L and Hall factor A _R differ significantly from universal constants π²/3 and 1, respectively, due to the pronounced energy dependence of the relaxation time during resonance scattering of carriers. The values of L and A _R are calculated for various values of the resonant impurity bandwidth, band filling with current carriers, and the relative contribution of resonance scattering. The available published data on the bandwidth of thallium impurity states in lead telluride, where intense resonance scattering of holes was observed, are discussed. The previously obtained data on the energy of Tl in PbTe resonant states were corrected taking into account the calculated Hall factor. An analysis of the experimental data on the dependence of the PbTe:Tl thermal conductivity on the temperature and content of additional Na dopant both showed that phonon scattering by polarized regions around charged impurity atoms is negligible and confirmed the results of theoretical calculations of the Lorentz number at dominant resonance scattering of holes.     

On the theory of anomalous photovoltage in multilayer structures with p-n junctions

Steady-and nonsteady-state photovoltages appearing in a multilayer structure with p-n junctions under the conditions of nonuniform illumination are considered for an arbitrary ratio between the diffusion length L and the sizes d of the p-and n-regions. It is shown that, for , the photovoltage is substantially lower (by d ²/12L ² times) than in the case of owing to the mutual influence of neighboring p-n junctions. Relaxation of the photovoltage is controlled by recharging of the barrier capacitances of p-n junctions, and the relaxation time exceeds by several orders of magnitude the lifetime of nonequilibrium charge carriers in the p-and n-regions. The results obtained make it possible to explain the special features of the effect of anomalous photovoltage in polycrystalline films.     

Fluid-to-cell assignment and fluid loading on programmable microfluidic devices for bioprotocol execution

Being a structure like a two-dimensional (2D) array of microvalves and cells, Programmable Microfluidic Device PMD biochips have the characteristics of reconfigurability and flexibility unlike conventional flow-based microfluidic biochips. In recent years, several design automation techniques for PMD biochips have been reported. For automated control of the PMD chip implementing a bioprotocol, one of the important tasks is to minimize the number of fluid flows for loading the reactant fluids into specific cells before the bioprotocol is executed. In this work we intensively study the fluid loading problem for PMD chips and we propose a two-phase approach to solve this problem. First, we propose a constraint satisfaction problem (CSP) based method, called loading-aware fluid-to-cell assignment (LAFCA) in order to obtain a suitable fluid-to-cell assignment, which will be beneficial for fluid loading phase. Then we propose an exact method, called CSP-based loading algorithm (CSPLA) and a near-optimal heuristic method, called determining flows from the last (DFL), for determining a sequence of fluid flows required to load different fluids into the cells of a PMD chip. We formulate CSPLA as a single objective optimization problem to minimize the total number of flows. For the output as a sequence of fluid flows we define three loading parameters, the total number of flows (K), the total number of 90° bends in all flow paths (B), and the total flow path length (L). Simulation results confirm that LAFCA combined with CSPLA outperforms (K, B and L reduced by 63.9%, 31.7% and 59.9%, respectively) the state-of-the-art method fluid loading algorithm for PMD (FLAP) [Gupta et al., TODAES, 2019]. Whereas, LAFCA combined with DFL can reduce the loading parameters K, B and L by 61.2%, 20.8% and 57.4%, respectively over using only FLAP. Also from the overall simulation results we can conclude that for many testcases, DFL can find the near-optimal Ks.