Fabrication of ZnO based MSM Photodetectors

The Project was successfully executed by Ms. Ghusoon Mohsin Ali, from Electronics Engineering Department, IT-BHU-Varanasi.

The project aims to fabricate a ZnO based UV photodetectors. This project is mainly divided into categories. First ZnO based metal-semiconductor-metal (MSM) UV photo detector with conventional interdigitated electrodes. In the second category the dark leakage current and sensitivity of ZnO based photodetector were improved by adding a SiO2 layer above ZnO thin film to achieve metal-insulator-metal (MIS) UV photodetectors with same interdigitated electrodes.

A photodetector is a device that converts the energy of photons into electrical energy, usually express as a photocurrent. Various types of photodetectors have been extensively studied for a long time, including photoconductive, avalanche, Schottky barrier, p-n junction, p-i-n junction,phototransitive, and metal-semiconductor-metal (MSM) photodetectors. Among these devices,MSM-based photodetectors offer various advantages such as fast, simplicity of fabrication, lowcapacitance per unit area, low dark current, low-noise, and high sensitivity. The metal-semiconductor-metal (MSM) structure consists of back-to-back Schottky contacts,separated by a layer of semiconductor, With Schottky contacts, dark current is determined by thermionic emission at the metal-semiconductor junctions.Following are the results attained at CEN.

Microscopy view of the substrate after developing

Microscopy top view of the MSM or MIS structure after metallization

SEM images for sol-gel thin film

To conclude ZnO thin films were grown on Si p-type (100) substrate by sol-gel method. ZnO MSM and MIS photodetectors were fabricated. Smaller dark current and larger photocurrent to dark current contrast ratio, lower ideality factor, larger barrier height from the ZnO MIS UV photodetector can be achieved.