Minority carrier decay length extraction from scanning photocurrent profiles in two-dimensional carrier transport structures

Carrier transport was studied both numerically and experimentally using scanning photocurrent microscopy (SPCM) in two-dimensional (2D) transport structures, where the structure size in the third dimension is much smaller than the diffusion length and electrodes cover the whole terminal on both sides. Originally, one would expect that with increasing width in 2D transport structures, scanning photocurrent profiles will gradually deviate from those of the ideal one-dimensional (1D) transport structure. However, the scanning photocurrent simulation results surprisingly showed almost identical profiles from structures with different widths. In order to clarify this phenomenon, we observed the spatial distribution of carriers. The simulation results indicate that the integrated carrier distribution in the 2D transport structures with finite width can be well described by a simple-exponential-decay function with the carrier decay length as the fitting parameter, just like in the 1D transport structures. For ohmic-contact 2D transport structures, the feasibility of the fitting formula from our previous 1D analytical model was confirmed. On the other hand, the application of a simple-exponential-decay function in scanning photocurrent profiles for the diffusion length extraction in Schottky-contact 2D transport structures was also justified. Furthermore, our simulation results demonstrate that the scanning photocurrent profiles in the ohmic- or Schottky-contact three-dimensional (3D) transport structures with electrodes covering the whole terminal on both sides will reduce to those described by the corresponding 1D fitting formulae. Finally, experimental SPCM on a p-type InGaAs air-bridge two-terminal thin-film device was carried out. The measured photocurrent profiles can be well fitted by the specific fitting formula derived from our previous 1D analytical model and the extracted electron mobility-lifetime product of this thin-film device is 6.6 × 10–7 cm2·V−1. This study allows us to extract the minority carrier decay length and to obtain the mobility-lifetime product which can be used to evaluate the performance of 2D carrier transport devices.

High-performance hysteresis-free perovskite transistors through anion engineering

Despite the impressive development of metal halide perovskites in diverse optoelectronics, progress on high-performance transistors employing state-of-the-art perovskite channels has been limited owing to ion migration and large organic spacer isolation. Herein, we report high-performance and hysteresis-free p-channel perovskite thin-film transistors (TFTs) based on methylammonium tin iodide (MASnI3) and rationalise the effects of halide (I/Br/Cl) anion engineering on crystallinity enhancement and vacancy suppression, realising a high hole mobility of 20 cm2 V−1 s−1, current on/off ratio exceeding 107, and threshold voltage of 0 V with high operational stability and reproducibility. We reveal ion migration has a negligible contribution to the hysteresis of Sn-based perovskite TFTs; instead, minority carrier trapping is the primary cause. Finally, we integrate the perovskite TFTs with commercialised n-channel indium gallium zinc oxide TFTs on a single chip to construct high-gain complementary inverters, facilitating the development of halide perovskite semiconductors for printable electronics and circuits.

Existence of Partially Degenerate Electrical Transport in Intermetallic Cu2SnSe3 Thermoelectric System Sintered at Different Temperatures

A detailed investigation on the temperature dependent electrical properties of Cu2SnSe3 system, synthesized via conventional solid-state reaction at different sintering temperatures are presented in this communication. All the samples exhibit degenerate semiconducting nature at low temperatures. The existence of small polarons and hence electron–phonon interactions are confirmed at temperatures below 400 K. A transition was observed from degenerate to non-degenerate semiconducting behaviour at high temperatures (T > 400 K). The study confirms the unusual transition in electrical resistivity as well as thermopower at high temperatures in all the compounds, demonstrating the existence of minority carrier excitation along with temperature-triggered ionisation of the defects. The transport behaviour is further supported by an upward movement of Fermi level away from the valence band. Highest weighted mobility of 8.2 cm2 V−1 s−1 at 673 K was obtained for the sample sintered at 1073 K. A considerable decrease in electrical resistivity with increase in temperature (T > 400 K) has driven the power factor to increase exponentially, thereby achieving highest value of 188 µV/mK2 (at 673 K) for the sample sintered at 673 K. Graphic abstract

Effect of Cooling Rate During Thermal Processes on the Electrical Properties of Cast Multi-Crystalline Silicon

Photoluminescence（PL）imaging techniques and the minority carrier lifetime test system were employed to investigate the variation of the interstitial iron (Fei) concentration, the recombination activity of structural defects and the minority carrier lifetime of cast multicrystalline silicon (mc-Si) in response to the cooling rate after heating. The results showed that when the mc-Si wafers are heated to high-temperature (1000 °C) and then cooled to ambient temperature with different cooling rate, the Fei concentration, the number of recombination active dislocations and grain boundaries increased as the cooling rate rises while the minority carrier lifetime decreased. If cast mc-Si is heated followed by faster cooling at 30 °C/s, the Fei concentration increase by 223% and the electrical activity of grain boundaries, dislocations and intragrain increase significantly, that is to say, the whole wafer is heavily contaminated with metal impurities, and present extremely low minority carrier lifetime.