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.
The deep UV photodetectors (DUV-PDs) are technologically important for diverse applications, ranging from environmental monitoring, space communication etc. Among all solar blind materials Ga2O3 thin film shows its strong contention owing to its intrinsic solar-blind nature. However, the PD’s efficiency can be significantly affected by the defects such as oxygen vacancies (VO). Both the deficiency and surplus of oxygen during Ga2O3 thin film deposition can result in the formation of carrier scattering centers, sub-bandgap absorption, and leakage channels. In this work, we have studied the impact of oxygen flow rate (OFR) on the optical and electrical properties of RF sputtered Ga2O3 thin film. The Ga2O3 thin films were deposited on p-Si at room temperature, where the Ar to O2 ratio has been varied from 1:0, 1:1, to 1:2 to maintain the O2 poor and O2 rich condition. The XRD spectrum shows the presence of two peaks positioned at ~33.0° , and ~64.5° , which are further identified as β(-202), and β(-313), respectively for samples grown without oxygen. The top view FESEM images confirm the uniform film growth for both O2 rich conditions while some isolated bubble-like and grain-like structures are witnessed in ratios 1:0, and 1:1, respectively. The change in optical bandgap for all the samples is determined using diffuse reflectance spectra which show the bandgap values lie in the range of 4.1 eV-4.2 eV. Furthermore, the deconvoluted photoluminescence spectra (in the range of λ=300-500 nm) show the change in different types of Vo defects originating due to OFR induced structural asymmetry in the Ga2O3 thin film. Finally, the change in dark current in Ga2O3/p-Si heterojunctions is estimated from current-voltage (I-V) characteristics to understand the effect of OFR on its electrical properties for future DUV detectors.
In the current study, we report the growth of rare earth Er-doped Ga2O3 nanostructures on Ga2O3- seeded Si substrate by employing chemical bath deposition (CBD) and RF magnetron sputtering techniques. A thin layer (~50 nm) of Ga2O3 is deposited on p-Si substrate with the optimize deposition temperature and Ar:O2 flow rate to create a favourable template for growing high quality nanostructures on it. After growing the Er-doped Ga2O3 nanostructures, thermal annealing is performed at 800°C to achieve thermodynamically stable β-phase of Ga2O3. The effect of Er doping on structural, optical and luminescence properties of Ga2O3 nanostructures has been successfully investigated by employing FEGSEM, XRD, UV-VIS and PL. XRD studies confirms the polycrystalline β-phase monoclinic structure of Ga2O3 for both undoped and Er-doped nanostructures with dominant <-111> plane. Top view images of FEGSEM depict the large area growth of rod/wire like structures of Ga2O3 on thin Ga2O3 deposited Si substrate and confirm the formation of heterojunction between Ga2O3 and Si. Deconvoluted PL spectra shows two broad peaks within the wavelength range of 260 nm to 460 nm, which are associated with near band emission and three different types of oxygen vacancies present in β-Ga2O3, respectively. The change in optical absorbance and corresponding energy band gap of undoped and Er-doped nanostructures are analysed in detail by using UV-VIS spectroscopy and such energy bandgap values lie with the range of 4.4 eV-4.7 eV. Finally, current-voltage characteristics of undoped and Er-doped Ga2O3/Si heterojunction has been studied and such heterojunctions can be a potential candidate for the fabrication of several optoelectronic devices as well as high power applications.
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