Validation of stable p-type phosphorus (P) doped ZnO thin films formation by investigating the photoresponse properties of P:ZnO/Ga2O3 heterojunctions

The formation of reproducible p-type conductivity in ZnO thin films is highly challenging now a days for the fabrication of several homo/heterojunction based fully transparent opto-electronic devices. In this study, p-type P: ZnO thin films are deposited by cost-effective SOD process and then intrinsically n-type Ga2O3 films are deposited on it to validate the p-type conductivity of ZnO by making vertical heterojunction with n-Ga2O3. The ZnO thin films are deposited by RF sputtering and subsequent P-doping is done by using the SOD technique on it. This involves proximity diffusing dopants into a spin-coated film by stacking the dopant source during thermal annealing at 800◦C for four hours in the furnace. Ga2O3 films are deposited on the P: ZnO films by using RF sputtering technique, for making the heterojunction. The electrical measurements are performed by using current-voltage (I-V) measurements under illuminated and dark conditions. The photo-switching and responsivity are also measured on the fabricated device. It is observed that the P: ZnO/Ga2O3 heterojunction exhibits the photoresponse in the dual wavelength region. The corresponding two peaks of responsivity are found around 200 nm and 390 nm with the values of 68.03 A/W and 7.93 A/W (at 5 V), respectively. Such two peaks originated due to the ultra-wide bandgaps of Ga2O3 (4.7eV) and P: ZnO (3.1 eV). Also, such heterojunction shows a rapid switching speed under white light at 5 V (rise time: 230 ms, fall time: 163 ms) and −5 V (rise time: 83 ms, Fall time: 169 ms), which is comparable with the other reported results. Therefore, the current study demonstrates the development of highly stable and reproducible p-type P: ZnO thin films by employing SOD technique and the validation of p-type formation by fabricating P: ZnO/Ga2O3 heterojunctions for dual-wavelength selector UV detector application and such detectors can be a potential candidate for various optoelectronic devices.