Electrical isolation of p-type GaAsN epitaxial layers by ion irradiation
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Electrical isolation of p-type GaAsN epitaxial layers by ion irradiation Q. Gao1, J. Muller2, P. N. K. Deenapanray1, H. H. Tan1, C. Jagadish1 1. Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia E-mail: [email protected] 2. FIUPSO, Université Paris Sud Orsay, Maison de l'ingénieur, 91400 Orsay, France ABSTRACT The evolution of sheet resistance (Rs) of p-type conductive GaAs(1-x)Nx epilayers (x = 0.6%, 1.4%, and 2.3%) exposed to MeV 1H+, 7Li+, 12C+, and 16O+ ions and the stability of the formed electrical isolation during post-irradiation annealing were investigated. Results show that the threshold dose (Dth) to convert a conductive layer to highly resistive one close-to-linearly depends on original free carrier concentration and inversely depends on the number of irradiation-generated atomic displacements, and is independent of the nitrogen content in GaAsN layers. Increasing beam flux of 12C+ results in a lower Dth , whereas 1H+ beam flux does not affect it, showing the influence of collision cascade density. Results also show that irrespectively of the ion mass, the stability of electrical isolation formed in GaAsN is dependent on the ratio of the concentration of irradiation-created carrier traps to Dth. The electrical isolation can be preserved up to 550ºC when the accumulated dose (D) is greater than 3.3 Dth. INTRODUCTION Dilute III-V nitride alloy semiconductors, for example, GaAsN and InGaAsN have drawn considerable attention in recent years [1-3], due to their unique physical properties (extremely large bowing parameter) and a wide range of potential applications, such as long-wavelength semiconductor lasers for optical communications [1], and heterojunction bipolar transistors (HBTs) [2-3]. Obviously, the fabrication of these devices needs various device-processing techniques. Ion implantation, a well-established technique, has been widely used for selective doping of semiconductor devices and electrical isolation [4, 5]. Electrical isolation of III-V semiconductors is now perhaps the most important application of ion implantation in this group of materials, due to the widespread use of epitaxial growth techniques for obtaining doped layers. The mechanism for the electrical isolation is generally believed to be the carrier trapping at damage-related deep level centers (defect isolation) or at chemical deep-level states (chemical isolation) [5]. Irradiation induced isolation has obvious advantages over mesa etching since it offers simplicity, precise depth control and retains the planarity of the surface. Electrical isolation using light mass ions (1H, 4He, 11B, 16O, etc.) has been proven to be a successful method to isolate neighbouring devices in compound semiconductor circuits, the degree of electrical isolation after ion irradiation and low temperature annealing is even superior than those provided by mesa etching [5]. Single energy MeV ion irradiation induced isolation
