Interfacial-Mixing and Band Engineering Induced by Annealing of CdS and a-Ga2O3 n-n-Type Thin-Film Heterojunction and Its Impact on Carrier Dynamics for High-Performance Solar-Blind Photodetection

Heterojunctions of dissimilar materialsare increasingly beingused in optoelectronics for their superior properties. However, theheart of the heterojunction its interface and its impacton the device performance are seldom studied in detail. Herein, wereport on the band alignment modification of heterojunction formedbetween amorphous Ga2O3 and CdS, two intrinsicallyn-type materials, with high optical absorbance but different bandgaps. The resultant heterostructure-based devices remain solar-blindand outperform the singular bare photodetectors. To further improveupon device performance, the heterostructure is subjected to a moderateannealing of 300 & DEG;C. The annealed heterojunction device showsa reduction in dark current by more than 1 order of magnitude alongwith an enhanced photocurrent. The response time of the devices reducesfrom 1.35 s/2.87 s (rise/fall time) to about 0.38 s/0.75 s upon annealing.To study this change in the device performance between the pristineand the annealed interface, the two heterojunctions are compared usingX-ray photoelectron spectroscopy depth profiling, and results showthat the pristine heterostructure has a sharp interface whereas uponannealing, it leads to a sort of diffuse interface. This producesa reduced valence band offset, resulting in a change in the band alignmentfrom type II to type I. The carrier dynamics across the two interfacestherefore changes and is further validated using Kelvin probe forcemicroscopy. This study reveals how the change at the interface bymere annealing can lead to a huge alteration in the band alignmentand thus, the carrier dynamics, thereby completely altering the ultimatedevice performance.

Automated summary

This study reports the band alignment modification of heterojunction formed between amorphous Ga2O3 and CdS. The annealed heterojunction device shows a reduction in dark current, enhanced photocurrent, and shorter response time. The changes at the interface due to annealing lead to a significant alteration in the band alignment and carrier dynamics, thereby completely altering the ultimate device performance.