Development of high-performance, low-cost integrated indium phosphide-based photoreceivers.

Abstract

Integration of InP-based photoreceivers has attracted much attention because of important applications in communication systems and potential advantages of integration. The InP-based photoreceiver is a key element in a fiber-optic communication system, which is the backbone of today's information superhighway. Integration can potentially reduce the size, weight, and cost of photoreceivers. Integration also enhances circuit reliability and reproducibility, and eliminates the undesired parasitic elements in the circuits. Integrated InP-based photoreceivers can deliver high-performance at a low cost only through an appropriate integration scheme. In this work, we propose a novel, compatible MSM-FET integration which employs ion implantation to overcome incompatibility between layer structures of FET's and MSM photodetectors. In the design, MESFET's and MSM photodetectors share a compatible layer structure, while the MESFET conducting channel is created by selective ion implantation. This integration scheme allows a simple fabrication process and does not degrade the device performance. In order to realize this scheme, we developed the key device, the first ion implanted InGaAs MESFET. A 1.5 $\mu$m gate length device exhibited a cut-off frequency of 19 GHz and a maximum frequency of oscillation of 70 GHz. High performance ion implanted InGaAs MESFET's are essential to the success of the proposed integration scheme. Another important device for this scheme is the InGaAs MSM photodetector. The device we fabricated had a 3dB bandwidth of 14.3 GHz with an electrode spacing/width of 1$\mu$m/1$\mu$m. This measurement was conducted by using an HP 83420 LightWave Test Set (LWTS) and an HP 8510B network analyzer. A two-dimensional numerical simulation was also developed for InGaAs MSM photodetectors. The simulation was based on a bipolar carrier model, in which Poisson's equation and current continuity equations are solved self-consistently. This integration scheme has been demonstrated for the first time. All individual elements in the circuits functioned well, including the transistors, photodetectors, capacitors, and resistors. A direct impedance photoreceiver with a load resistor of 100 $\Omega$ exhibited a 3 dB bandwidth of 10.5 GHz when the FET was biased in the linear region and a bandwidth of 2.5 GHz when the FET was biased in the saturation region. In summary, a novel integration scheme has been proposed and developed for InP-based photoreceivers. The results obtained are excellent for the geometries employed and improved performance can be obtained by utilizing submicron technologies which already exist.