Transient photoconductivity probe data of morphology-induced Bismuth-Oxysulfide obtained at 120 GHz

Bismuth-Oxyselenide as we know, is an indirect band gap high electron mobility layered material behaving as a 2D Van der Waals with the band-gap ~0.8 eV. This material has become an important candidate for its use as an electronic/optoelectronic material. However, its sister candidate, Bismuth Oxy-Sulfide with band gap 1.1 eV is less studied and also has potential to become a strong material for photodetection, and photocatalytic applications. For this purpose, in the year 2023, we studied the in-house fabricated (drop casted) nanosheet samples1 using the time-resolved millimeter wave conductivity (TRmmWC) system2 once with, and another time without HH. We note morphology-induced photoconductivity modulation of these nanostructures when hydrazine hydrate (HH) thins out the structure itself, resulting in faster carrier trapping time. HH is expected to reduce the number of deep traps resulting in slow initial decay, and also induce narrow tail states, higher mobility, and also suppressed thermal hopping mechanism in the sample. TRmmWC is more sensitive to the charge carriers than the excitons; Zero-bias Schottky diode (ZBD) with a responsivity ~ 1.6 V/W and 3.2V/mW are used for signal detection in transmission and reflection arrangements, respectively. Stimulus of Bi2O2S is provided using a 532 nm DPSS laser with a pulse-width of 0.69 ns repeated every millisecond. Intensity of this laser provides a fluence 10.1µJ/cm2 with a spot size ~ 23.75 square mm and probed with D-band signal with a pot size approximately 6.6 square mm (ratio: ~4:1). The idea of performing this experiment was to collect probe data that denotes changes in photoemission induced transmission voltages (RF transients) and dark (no laser stimulus) dc responses of Bi2O2S transmitted through sample at 120 GHz. An Elva-1 cavity-stabilized IMPATT diode oscillator (CIDO) was operated to provide the probe signal to the open-air TRmmWC system2. The RF output files comprise three data files: one on the data obtained when the nanosheet sample has no HH, another with the sample having HH, and a background file. The background file needs to be subtracted from the signal file each time any numerical analysis is performed. These files are ASCII-delimited comma-separated variable (.csv) files obtained after low noise amplification (LNA) with a gain of 35.7 and averaging about 10,000 times. Column 1 represents the delay (seconds), and column 2 is the RF voltage (Volts) after amplification. The DC transmission voltages (120 GHz) through sample when laser is off/on for sample with HH -327.7mV/-289mV, and without HH: -326.4mV/-326.6mV. Due to the presence of HH in these nanosheets, crystallinity is boosted, and the fitted parameters (in Ref. 1) suggest that HH induces rapid carrier trapping. A refined modeling study might be useful for a comparison.