A Perspective on Nanowire Photodetectors: Current Status, Future Challenges, and Opportunities

One-dimensional semiconductor nanostructures (nanowires (NWs), nanotubes, nanopillars, nanorods, etc.) based photodetectors (PDs) have been gaining traction in the research community due to their ease of synthesis and unique optical, mechanical, electrical, and thermal properties. Specifically, the physics and technology of NW PDs offer numerous insights and opportunities for nanoscale optoelectronics, photovoltaics, plasmonics, and emerging negative index metamaterials devices. The successful integration of these NW PDs on CMOS-compatible substrates and various low-cost substrates via direct growth and transfer-printing techniques would further enhance and facilitate the adaptation of this technology module in the semiconductor foundries. In this paper, we review the unique advantages of NW-based PDs, current device integration schemes and practical strategies, recent device demonstrations in lateral and vertical process integration with methods to incorporate NWs in PDs via direct growth (nanoepitaxy) methods and transfer-printing methods, and discuss the numerous technical design challenges. In particular, we present an ultrafast surface-illuminated PD with 11.4-ps full-width at half-maximum (FWHM), edge-illuminated novel waveguide PDs, and some novel concepts of light trapping to provide a full-length discussion on the topics of: 1) low-resistance contact and interfaces for NW integration; 2) high-speed design and impedance matching; and 3) CMOS-compatible mass-manufacturable device fabrication. Finally, we offer a brief outlook into the future opportunities of NW PDs for consumer and military application.

I. Introduction

Traditional R&D activities in photodetectors (PDs) have been largely focused on pursuing miniaturized PDs with high responsivity, large bandwidth, short response time, low noise, and high gain-bandwidth. PDs such as p-n junctions, p-i-n diodes, phototransistors, and avalanche photodiodes are some of the depletion-mode devices widely used in photoreceivers because of their low operational voltages, high sensitivity, and high-speed properties. The absorption coefficient of the active layer material in a PD is typically ∼1/ μm. In order to ensure substantial absorption of the incident light, and thus, increase the sensitivity and quantum efficiency, the thickness of the active layer of conventional PDs has to be designed accordingly. As an example, in order to achieve quantum efficiency greater than 80%, GaAs PDs need more than 1.8-μm absorption layer thickness (when λ_absorption is 840 nm), which is thicker than the dimensions of most thin-film-based devices used in electronics and optoelectronics.