Quantum mechanical tunnelling: the missing term to achieve sub-kJ mol−1 barrier heights

Quantum tunnelling can lower the effective barrier height, creating a discrepancy between experiment and theory.

Excitation Intensity and Temperature-Dependent Performance of InGaN/GaN Multiple Quantum Wells Photodetectors

In this article, we investigate the behavior of InGaN–GaN Multiple Quantum Well (MQW) photodetectors under different excitation density (616 µW/cm2 to 7.02 W/cm2) and temperature conditions (from 25 °C to 65 °C), relating the experimental results to carrier recombination/escape dynamics. We analyzed the optical-to-electrical power conversion efficiency of the devices as a function of excitation intensity and temperature, demonstrating that: (a) at low excitation densities, there is a lowering in the optical-to-electrical conversion efficiency and in the short-circuit current with increasing temperature; (b) the same quantities increase with increasing temperature when using high excitation power. Moreover, (c) we observed an increase in the signal of photocurrent measurements at sub-bandgap excitation wavelengths with increasing temperature. The observed behavior is explained by considering the interplay between Shockley–Read–Hall (SRH) recombination and carrier escape. The first mechanism is relevant at low excitation densities and increases with temperature, thus lowering the efficiency; the latter is important at high excitation densities, when the effective barrier height is reduced. We developed a model for reproducing the variation of JSC with temperature; through this model, we calculated the effective barrier height for carrier escape, and demonstrated a lowering of this barrier with increasing temperature, that can explain the increase in short-circuit current at high excitation densities. In addition, we extracted the energy position of the defects responsible for SRH recombination, which are located 0.33 eV far from midgap.

Electrical properties of Ga-doped ZnO nanowires/Si heterojunction diode

Herein, we report the high-temperature electrical characteristics of heterojunction diode fabricated based on n-Ga-doped ZnO nanowires/p-Silicon substrate. Various electronic properties such as rectification ratio, the effective barrier height, the diode ideality factor, etc. of the fabricated heterojunction diode at high temperature were investigated. The electrical characteristics were examined in the high-temperature range of 293 K–433 K in both reverse and forward biased conditions, which exhibited good stability over the entire temperature range. The observed current–voltage (I–V) studies confirmed three different conduction mechanisms for the fabricated heterojunction diodes, i.e., either field emission or tunneling, recombination-tunneling mechanism and the transport mechanism dominated by space-charge-limited current at the different regions. The observed electrical results exhibited fluctuations in the sensitivity of the quality factor of the heterojunction diode and consequently corresponding fluctuations in the resistance. The linear dependence of effective barrier height on quality factor can be attributed to the presence of some lateral inhomogeneities in the barrier height. The analysis of C–V data was conducted to deduce the value of barrier height of Schottky barrier for the fabricated heterojunction diode. Interestingly, the observed results assert the mismatch that occurs between the interface states and resulting capacitance of the fabricated heterojunction diode.

Coordination polymers of a bis-isophthalate bridging ligand with single molecule magnet behaviour of the CoII analogue

A Co(ii) coordination polymer shows SMM behaviour with an effective barrier height among the highest reported for such materials.

Electronic parameters of MIS Schottky diodes with DNA biopolymer interlayer

In this work, we prepared an ideal Cu/DNA/n-InP biopolymer-inorganic Schottky sandwich device formed by coating a n- lP semiconductor wafer with a biopolymer DNA. The Cu/DNA/n-InP contact showed a good rectifying behavior. The ideality factor value of 1.08 and the barrier height (Φb) value of 0.70 eV for the Cu/DNA/n-InP device were determined from the forward ias I-V characteristics. It was seen that the Φb value of 0.70 eV obtained for the Cu/DNA/n-InP contact was significantly larger tan the value of 0.48 eV of conventional Cu/n-InP Schottky diodes. Modification of the interfacial potential barrier of Cu/n-InP iode was achieved using a thin interlayer of DNA biopolymer. This was attributed to the fact that DNA biopolymer interlayer increased the effective barrier height by influencing the space charge region of InP.

MICROSTRUCTURE AND NONOHMIC PROPERTIES OF SnO2–Ta2O5–ZnO BASED CERAMIC VARISTORS DOPED WITH TiO2

The microstructure and nonohmic properties of SnO 2– Ta 2 O 5– ZnO based ceramics sintered at 1450°C for 2 h were investigated in accordance with TiO 2 content (0–8 mol%). Without TiO 2 the prepared sample is nonstoichiometric SnO 2 semiconductor with excessive oxygen; but for the samples doped with TiO 2, Sn 0.9 Ti 0.1 O 2 phase can be identified, and the incorporation of TiO 2 into the ternary system SnO 2– Ta 2 O 5– ZnO ceramics can compensate the defects of Sn 4+ ions loss, promote the sample densification, and facilitate the growth of SnO 2 grains. After 4.0 mol% of TiO 2 is doped, the samples present no precipitated substances residing in the grain juncture, resulting in varistors with maximum nonlinear exponent of 21, varistor voltage of about 1000 V/mm, and minimum leakage current of 100 μA/cm2, which are promising in high-voltage applications. The improvement in nonohmic performance of the varistors after the doping of TiO 2 is mainly attributed to the increase in effective barrier height in grain boundary, which can be supported by the decrease in band gap caused by defects and impurities from periodic density function theory calculation.