Study of long‐term stability of ohmic contacts to GaN

Abstract

We report on low-resistivity thermally stable ohmic contacts to p-GaN using ZrN/ZrB 2 metallisation. Transport properties, thermal conductivity and long-term stability of contacts were examined. pGaN/ZrN/ZrB 2 contacts show excellent stability upon aging in air, indicating their suitability for longterm operation at temperatures up to 150 ºC.1 Introduction GaN's intrinsic properties such as wide bandgap, high thermal conductivity, high melting temperature, high breakdown voltage and high saturation velocity make it a material of choice for high temperature and high power electronic devices [1]. During the last decade, significant progress in both material and processing technologies as well as in the design of new device structures has been made. Now the most important and challenging problem is to master the reliability of GaN-based devices.In this paper we address the issue of long-term stability of ohmic contacts to GaN. Electrical contacts that are structurally stable at high temperature are the prerequisite for reliable operation of GaN electronic devices. Zr-based metallisation was chosen as a contact material because of high electrical conductivity, superior thermal stability and chemical resistance against corrosion, making it compatible with GaN. Zr/ZrN metallisation was reported effective in providing low-resistivity contacts to n-type GaN by depleting its superficial film from nitrogen, creating thus a highly doped subcontact region and a stable ZrN compound at the contact interface [2]. In our previous studies, ZrN/ZrB 2 metallisation was used for p-type GaN contacting purposes. The presence of Zr in the metallisation was a key factor for the formation of the ohmic contact by removal hydrogen from the subcontact layer and creation thereby a highly doped p + region [3]. Moreover, structural stability of ZrN/ZrB 2 metallisation deposited on GaN upon annealing up to 1100 °C in N 2 has been proven [4]. In the present study we have investigated the thermal conductivity of p-GaN/ZrN/ZrB 2 ohmic contacts and performed accelerated lifetime testing of these contacts. It is well established that efficient heat removal is critical to the performance of semiconductor devices. Thus for thermal management of the device, it is important to know accurately the value of the thermal conductivity of metallisation and semiconductor subcontact region. Thermal conductivity investigations were performed using Scanning Thermal Microscopy (SThM), enabling to couple the topographic image with the thermal conductivity information [5]. To age the contacts they were annealed in air at temperatures up to 150 °C over a period of 300 hours. The aging process was monitored by specific contact resistance measurements and compositional depth profiling of the contacts.

50 Years of Compounds Semiconductors at the Institute of Electron Technology, Warsaw

“…• Copernicus '95, the subject of which were tunable GaInAsSb/AlGaAsSb DH laser diodes for environmental pollutions control [45] (iii) fabrication of metal/oxide multilayer structures for interferometric studies and SnO 2 and ZnO diffractive elements for nanostructured gas sensors [65][66][67][68]; (iv) novel approaches to the fabrication of ohmic contacts to GaN [69][70][71][72][73][74][75][76][77][78][79][80], e.g., n-type doping by creating nitrogen vacancies in the contact region of Ti-based metallizations [69], enhanced activation of the Mg acceptor to increase p-type doping of subcontact region of the ZrN/ZrB 2 ohmic contacts [70], nand p-type doping via solid phase regrowth (SPR) for the ohmic contacts to n-and p-GaN [71,72], engineering ZnO/GaN interface for the transparent ohmic contact to p-GaN [73,74], engineering electronic structure of p-GaN surface via appropriate surface preparation procedure [75], advanced refractory metal-based metallizations with enhanced antidiffusion capabilities [76][77][78][79][80]; (v) passivation of GaN-based heterostructures by a thin film of ZnO [81].…”

NiO removal of Ni/Au Ohmic contact to p-GaN after annealing

“…GaN's intrinsic properties such as wide bandgap, high thermal conductivity, high melting temperature, high breakdown voltage, and high saturation velocity [1] make it a material of choice for ultraviolet and visible wavelength optoelectronic devices. In the past decade, significant progress in material growth and processing technologies and in new device design has been made.…”