Timothy A. Vang

Integrated inversion channel optoelectronic devices and circuit elements for multifunctional array applications

An approach to laser-based optoelectronic integration is described. It is shown that by using a single epitaxial growth structure and a common processing sequence, all the electrical and optical devices required for a complete optoelectronic integrated circuit (OEIC) are realized. The demonstrated individual device performance and the implementation of an integrated combination of devices are discussed. Such applications as the implementation of a basic building block for a 2*2 smart-pixel switching node are discussed. A comparison to other laser- and modulator-based approaches is presented. >

Demonstration of the heterostructure field‐effect transistor as an optical modulator

A new semiconductor waveguide absorption modulator is demonstrated utilizing the heterostructure field‐effect transistor structure. The modulator of 300 μm length and 10 μm width achieves an extinction ratio of 8 for a gate voltage change of 2.5 V and an absorption change greater than 2300 cm−1. The transistor transconductance is 92 ms/mm for a 1 μm device and an identical structure has been reported as an edge‐emitting laser providing an ideal combination for optoeletronic integration.

A quantum-well inversion channel heterostructure as a multifunctional component for optoelectronic integrated circuits

An approach to optoelectronic integration utilizing a universal heterostructure with a single GaAs quantum-well active region is presented. The inversion channel forms the basis of a heterojunction field-effect transistor, a lateral current injection laser, a field-effect modulator, and a waveguide photodetector by simple reconfiguration of the electrodes and device geometry. The fabrication technology has been developed for gigahertz bandwidth applications by utilizing ion implantation techniques for interdevice electrical isolation and surface planarization, and reactive ion-etching to realize a self-aligned transistor-based heterostructure. The design, fabrication, and characterization of various heterostructures are discussed in the context of optoelectronic integration and the implementation of ion implantation disordering to realize low-loss self-aligned waveguides for on chip signal routing. The ultimate performance of the devices using a GaAs quantum well is considered, as well as the development of this technology for improved performance using strained InGaAs wells. >

Heterostructure field‐effect transistor optical modulator in the InGaAs/AlGaAs material system

The heterostructure field‐effect transistor optical modulator is demonstrated in a waveguide geometry using strained InGaAs quantum wells. A 20 μm×300 μm device is shown to have a contrast ratio of 35:1 using a 2 V swing from −1 to +1 V, which results in a figure of merit of 25.7 dB/V mm for this device. A Kramers–Kronig transformation is used to show the potential low chirp available at maximum contrast ratio for this device. Wavelength compatibility with a 5 μm×400 μm heterostructure field‐effect laser from the same wafer is demonstrated, and the corresponding heterostructure field‐effect transistor is also demonstrated from the same wafer with a transconductance of 120 mS/mm for a 1 μm gate length.

High quantum efficiency strained InGaAs/AlGaAs quantum‐well resonant‐cavity inversion channel bipolar field‐effect phototransistor

A high‐efficiency, resonant‐cavity, bipolar inversion channel field‐effect transistor detector is demonstrated with a triple‐strained InGaAs quantum‐well absorbing region. A quantum efficiency of 80% is obtained at a resonant wavelength of 0.94 μm, and a bandwidth of 20 A, giving a 26‐fold enhancement in absorption due to resonance. The transistor detector operates in the FET mode with an independent gate electrode to control its sensitivity, and in a bipolar mode with a photogain of 25. The structure is identical to that used in other inversion channel laser structures, and hence provides an optimum configuration for optoelectronic integration. This is the first demonstration of a three‐terminal quantum‐well resonant‐cavity photodetector.

Operation of a single quantum well heterojunction field‐effect photodetector

The single quantum well heterojunction field‐effect photodetector is demonstrated for the first time as a GHz bandwidth waveguide heterostructure, and as the optoelectronic counterpart to the single quantum well heterojunction field‐effect transistor. For a 1 μm gate‐length device a responsivity of 0.16 A/W, external quantum efficiency of 0.35, and test‐laser limited rise time of 100 ps are obtained.

Quantum well lasers with carbon doped cladding layers grown by solid source molecular beam epitaxy

Data are presented which demonstrate that very high quality carbon (C) doped epilayers for the fabrication of AlGaAs‐GaAs and AlGaAs‐GaAs‐InGaAs quantum well (QW) lasers can be grown by solid source molecular beam epitaxy (MBE) using a resistively heated graphite filament as a p‐type dopant source. Broad area lasers fabricated from this material exhibit very low threshold current densities (66 A/cm2 for a 2‐mm‐long single QW AlGaAs‐GaAs‐InGaAs laser emitting at 980‐nm wavelength). It is also shown that lasers with carbon doped cladding layers grown on either n+ or p+ substrates exhibit similar low threshold current densities. These C‐doped lasers are expected to have improved long term reliability compared to conventional Be‐doped laser structures.

The inversion channel resonant-cavity enhanced photodetector for two-dimensional optoelectronic array applications

The operation of the inversion-channel resonant-cavity enhanced (RCE) photodetector in a configuration compatible with the vertical-cavity surface-emitting laser (VCSEL) is discussed. The phototransistor uses three strained InGaAs/GaAs quantum wells as the absorbing region and a post-growth dielectric top stack. A quantum efficiency of 41% was obtained at the resonant wavelength of 0.94 mu m, thereby giving a resonant-enhancement factor of 13.5. A bipolar transistor gain of 6.8 at a current density of 10 A/cm/sup 2/ allowed the phototransistor responsivity to reach 2.1 A/W at the resonant wavelength.<<ETX>>

Electronic/photonic inversion channel technology for optoelectronic ICs and photonic switching

A new approach to optoelectronic integration is presented in which all optical and electronic devices are derived from a single crystal growth and a single fabrication sequence. The approach uses a self-aligned inversion channel capable of functioning as an FET or bipolar transistor, a detector, a modulator or a laser in either an analog or a digital mode. Topics discussed include a three-terminal switching laser, a bipolar inversion channel field-effect transistor, a three-terminal analogue laser, an HFET detector, and an HFET optical modulator.

Inversion channel detection circuits for optoelectronic interconnect

The inversion channel technology is a new approach to monolithic optoelectronic integration that offers the possibility of FET logic, optical detection, and laser emission from a single chip. The detection is performed by the three terminal configuration of the DOES biased in the off state. Incident light switches the DOES into the on state and recovery from the on state is provided by the conduction of electrons from the inversion channel through a FET connected to the third terminal. In this paper we demonstrate the functionality of this operation with an OEIC that integrates the three terminal DOES device with four FETs. The operation is discussed both as an optical clock and as an electrically clocked optical gate. Sensitivity issues are considered.