Pt/n-GaN metal-semiconductor and Pt/HfO2/n-GaN metal-insulator-semiconductor Schottky diodes
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Pt/n-GaN metal-semiconductor and Pt/HfO2/n-GaN metal-insulator-semiconductor Schottky diodes Arjun Shetty1, Basanta Roul2, Shruti Mukundan2, Greeshma Chandan2, Lokesh Mohan2, K J Vinoy1, S B Krupanidhi2 1 2
Electrical Communication Engineering, Indian Institute of Science, Bangalore, India Materials Research Centre, Indian Institute of Science, Bangalore, India
ABSTRACT Gallium nitride (n-type) films of thickness 300nm were grown on c-plane sapphire substrates using plasma assisted molecular beam epitaxy (PA-MBE). High resolution X-ray diffraction and photoluminescence measurements were used to confirm the crystalline and optical qualities of the grown films. Metal-semiconductor Schottky diodes were fabricated using Pt as the Schottky metal and Al as the Ohmic metal contact. Metal-insulator-semiconductor Schottky diodes were also fabricated using HfO2 (10nm) as the insulator material. Diode parameters like barrier height and ideality factor were extracted from I-V measurements. Introduction of HfO2 as the insulator layer leads to better rectifying behavior (forward to reverse current ratio improves from 5.1 to 8.9) with a reduction in reverse leakage current (by 7.4 times), increase in barrier height (from 0.62eV to 0.74eV) and a reduction in ideality factor (from 6 to 4.1) of the Schottky diode. INTRODUCTION Moore’s law [1] has been sustained for over 30 years due to continuous scaling of transistors. Scaling down of devices is the primary driving force and the physical gate length has already reached 30nm in the current 65nm technology node and is expected to reach 10nm within the next few years [2]. Beyond this, quantum effects tend to become prominent and we get diminishing returns from scaling at the cost of increased fabrication complexity. It is imperative that we look at alternative materials to scaling in order to continue enjoying the benefits of Moore’s law. Gallium nitride (GaN) offers unique advantages over other materials for high frequency and high power applications like larger peak electron velocity, larger saturation velocity, higher breakdown voltage and thermal stability [3-6], making it ideal for use as a channel material in microwave and high frequency integrated circuits. Successful realisation of these devices requires Schottky contacts with large Schottky barriers and good thermal stability. The wide and direct bandgap (3.4eV) of GaN results in a lower leakage current and consequently, an ability to operate at higher temperatures. Schottky diodes have advantages like high operating frequency, fast switching speed and low forward voltage drop. As a result, Schottky diodes are widely used in a variety of RF and microwave applications like varactors, detectors, mixers, multipliers and low-voltage reference circuits. The conventional Schottky contact consists of a direct contact between the metal and the semiconductor resulting in a metal-semiconductor (MS) Schottky barrier diode. However, in
practice there is always a thin interfacial layer of oxide between the metal and the semiconductor r
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