SGER: New Approach to Revolutionize a Photovoltaic Detector Performance Using Electron Injection-Induced Effects in AlGaN

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

Wide band gap GaN-based semiconductors are attracting increasing attention due to their importance in modern electronics. The applications of GaN necessitate the controlled modification of its fundamental electronic properties, in addition to the availability of high quality material. The spectral response of the GaN-based photovoltaic detectors is generally limited by the large absorption coefficient at high energies and the small minority carrier diffusion length. Recent design changes, to overcome these limitations, include the use of p-i-n instead of p-n junction [1-4], substitution of GaN by AlxGa1-xN [1-3] or semitransparent recessed windows [2], and a back-illuminated detector configuration [3]. However, a tuning of fundamental (Al)GaN properties, to boost the performance of III-Nitride devices, was never directly considered. The innovation in this proposal is to significantly enhance a photovoltaic detector performance by tailoring the minority carrier diffusion length in (Al)GaN. The diffusion length is a crucial parameter for the detector quantum efficiency and photoresponse. The underlying concept is defined by the PI.s recent findings [5-8] that electron injection into p-(Al)GaN from the application of an external voltage in a solid state device--p-n junction or Schottky barrier-increases the critical minority carrier diffusion length and lifetime. Consistent changes were observed in other material properties, including luminescence and spectral photoresponse, and were attributed to charging of deep metastable Mg-acceptor-related centers [6]. The practical significance of this research is a long-term (days), revolutionary (up to an order of magnitude!) performance enhancement for (Al)GaN-based photovoltaic detectors, achieved through short time (at most 1500 sec) electron injection. This is because the increased diffusion length improves minority carrier collection and eliminates the "dead space", where carriers recombine before they are collected. The proposed project is of high risk, since it must be determined whether the novel electron injection-induced effects in p-(Al)GaN [5-8] are universal in nature and represent a fundamental property of the p-type material, or if instead they depend on the material's quality, growth, and processing conditions. If, indeed, the effects are universal, a high pay off will be manifested in a development of this novel and simple approach to revolutionize photovoltaic detector performance by manipulating the material.s transport properties, which will likely be used in combination with design and technology improvements. Success in this SGER application will lead to the implementation of this approach in commercial detectors, and will advance the frontiers of this technology for use in other bipolar devices for which the diffusion length is critical (transistors, thyristors) [6]. It is planned to submit a GOALI proposal (with Corning) based on success of this project. The broader impact of this research will be a dipper understanding of electron transport in GaN and related compounds, the integration of research with education, and partnership with industry.