| Wide bandgap material provides a good solution for high sensitivity detection of photons in the ultraviolet (UV) and near-UV spectrum. AlGaN based photodetectors have great potential to be of practical and commercial importance in various applications, including sensing, communication and detection, due to its superior intrinsic property.;An AlGaN-based Schottky photodiode was designed, fabricated and characterized. The wafer for fabrication of Schottky photodiodes was grown on single-side polished c-plane (0001) sapphire (Al2O3) substrate by Plasma assisted Molecule Beam Epitaxial (MBE) technique. Before fabrication of the devices, the material was characterized by X-Ray Diffraction (XRD) and Cary 500 Spectrometer to measure the thin film quality and transmission spectrum, respectively.;In addition to a standard photolithography technique, Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) was used in the formation of the double-mesa structure during the fabrication process due to the inert chemical nature of AlGaN. Then Ti/Al/Ti/Au metal composite was deposited to the bottom of the mesa and annealed at 800°C for 5 minutes in a Rapid Thermal Annealing (RTA) system to form n-type Ohmic contact between the n+-AlGaN layer and metal. Spin-on-glass (SOG) was applied over the sample using a spinner to act as the dielectric insulating layer between the bottom and top contacts. An Oxygen (O2) plasma treatment was performed to completely oxidize the SOG by filling the vacancies in SOG, which otherwise would become soluble in AZ 400K developer. CF4 was used as the reactive gas to etch the SOG using ICP-RIE, in order to open windows for metallization on the top of the device. After this, Ni/Au was deposited to form Schottky contact between the n--AlGaN layer and metal. The following step was packaging the device on oxygen free copper plate and wire bonding to connect the bottom and top contacts of the devices to the bars.;Then the probe station was used to measure the I-V characteristics of the Schottky photodiodes, including dark current and photo current. To conduct photo current measurement, a 2 uw/cm2/nm DH-2000 CAL light source, which could provide UV light from 220 nm to 400 nm, was used. |
