High performance waveguide uni-travelling carrier photodiode grown by solid source molecular beam epitaxy.

Xiaoli Lin,Jiang Wu,Michele Natrella,Chris Graham,Cyril C Renaud,Alwyn J Seeds,Mingchu Tang,Huiyun Liu,James Seddon

doi:10.1364/oe.27.037065

Abstract

The first waveguide coupled phosphide-based UTC photodiodes grown by Solid Source Molecular Beam Epitaxy (SSMBE) are reported in this paper. Metal Organic Vapour Phase Epitaxy (MOVPE) and Gas Source MBE (GSMBE) have long been the predominant growth techniques for the production of high quality InGaAsP materials. The use of SSMBE overcomes the major issue associated with the unintentional diffusion of zinc in MOVPE and gives the benefit of the superior control provided by MBE growth techniques without the costs and the risks of handling toxic gases of GSMBE. The UTC epitaxial structure contains a 300 nm n-InP collection layer and a 300 nm n++-InGaAsP waveguide layer. UTC-PDs integrated with Coplanar Waveguides (CPW) exhibit 3 dB bandwidth greater than 65 GHz and output RF power of 1.1 dBm at 100 GHz. We also demonstrate accurate prediction of the absolute level of power radiated by our antenna integrated UTCs, between 200 GHz and 260 GHz, using 3d full-wave modelling and taking the UTC-to-antenna impedance match into account. Further, we present the first optical 3d full-wave modelling of waveguide UTCs, which provides a detailed insight into the coupling between a lensed optical fibre and the UTC chip.

Highlights

TERAHERTZ (THz) band frequencies, located between microwaves and infrared in the electromagnetic spectrum (100 GHz to 10 THz), possess unique properties which can enable important potential applications in spectroscopy, material science, medical science, security imaging and high-speed wireless communication
Photonic techniques can benefit from signal transmission over optical fibre cables, allowing THz modulated optical signals to be distributed over long distances
The Uni-Travelling Carrier Photodiodes (UTC-PDs) epitaxial structure grown by solid-source MBE (SS-MBE) for this work is the same as the one we reported in [8], which was intended to achieve band gap engineering improvements and more precise doping profiles than our previous work using Metal Organic Chemical Vapour Deposition (MOCVD) [13]

Summary

Introduction

TERAHERTZ (THz) band frequencies, located between microwaves and infrared in the electromagnetic spectrum (100 GHz to 10 THz), possess unique properties which can enable important potential applications in spectroscopy, material science, medical science, security imaging and high-speed wireless communication. UTC-PDs generate higher output saturation current due to the reduced space charge effect in the depletion layer, which results from the high electron velocity in the depletion layer [6]. Fabricated vertically illuminated UTC-PDs exhibited 0.1 A/W responsivity at 1550 nm, 12.5 GHz 3 dB bandwidth and −5.8 dBm output power at 10 GHz, at a photocurrent of 4.8 mA. Though vertically illuminated UTC-PDs have shown improved 3 dB bandwidth, their geometry requires a stringent trade-off between DC responsivity and bandwidth For such a normalincidence structure, high responsivity requires a thick absorption layer, which results in increased carrier transit time and reduced device bandwidth. For a given device area and epitaxial structure (i.e. same bandwidth), a waveguide coupled UTC-PD can exhibit higher output power than a vertically illuminated UTC-PD at high frequency [9,10]. We present a comprehensive optical 3d full-wave modelling analysis of the fibre-to-chip coupling

Structure growth and device fabrication

Optical 3d full-wave modelling

Coplanar waveguide coupled UTC-PDs

Antenna integrated waveguide UTC-PDs

Findings

Conclusion