This research program applies photoluminescence (PL), photoluminescence excitation spectroscopy, time-resolved PL and PL imaging to the characterization of defects and impurities in bulk and epitaxial semiconductor materials; the composition, doping, thickness, interfaces, and uniformity of layered semiconductor heterostructures; rare earth-doped semiconducting glasses; and the effects of patterning and fabrication processing steps on the electronic and optical properties of photonic and optoelectronic devices.

The Center for Optoelectronics Science and Technology (COST) comprises a consortium of engineering faculty from UIUC, University of Michigan, and University of Texas. The COST research program includes: optoelectronic (OE) systems integration; OE software tools; optimal specifications of OE devices; OE systems testbeds; materials issues for OEIC packaging; integrable, reliable, temperature-invariant and tunable lasers; multiwavelength lasers and arrays for WDM; processing for laser fabrication; ultrashort pulse lasers; high-speed optical pulse shapers; hybrid receivers for 1550 nm; GaAs MSM/MESFET OEIC receivers (single and multichannel arrays); SiGe/Si receivers; and InGaAs/InP HBT-based OEIC receivers.

iPOINT is the Illinois pulsar-based optical interconnect testbed in which a multitude of high-power workstations are connected with broad bandwidth optical fibers, photoreceivers, and optical transmitters. This project is carried out in collaboration with the Department of Computer Science and is linked with AT&T's Blanca gigabit network project. This project provides systems-driven specifications for optoelectronic devices and testing environment for fabricated devices. At the same time, new architectures and systems applications are investigated based on opto electronics technology.

The objective of this project is to develop the gas source molecular beam epitaxy (GSMBE)/chemical beam epitaxy (CBE) technique for the growth of phosphorous-containing III-V compounds and alloys and demonstrate the suitability of the technique for the growth of multilayer heterostructures and heterojunctions required for ultrahigh frequency devices and high-efficiency photonic devices. The growth process will be optimized to yield improvements in the epitaxial layer purity, interface quality, reproducibility and uniformity of composition, thickness and doping, and a reduction of the surface defect concentration.

This program investigates III-V semiconductor quantum-wire (QWR) structures grown by solid and gas source molecular beam epitaxy. Spontaneous strain-induced lateral layer ordering process which occurs during growth of short- period superlattice heterostructures will be used to prepare the QWR structures with the wire size of less than 100Å × 100Å. The influence of the growth conditions, such as the growth temperature, the V/III flux ratio, and the magnitude of the strain on structural and optical properties of the QWR structures will be studied.

Multiple-layer heterostructure devices such as HEMTs and HBTs have shown great promise recently as devices for optoelectronic integrated circuit (OEIC) receiver applications. In this project, various heterojunction OEIC structures will be prepared, characterized, and optimized. The short wavelength (0.85 µm) and long wavelength (1.3 ~ 1.55 µm) OEIC receivers based on HEMT and HBT technologies will be grown by solid source and gas source MBE, respectively, using either the highly developed AlGaAs/GaAs materials system or the advanced AlInAs/GaInAs/InP and GaInAsP/InP heterostructure materials systems.

Novel materials and processes for long and mid-wave infrared (IR) detectors are the focus of this investigation. When a Schottky contact is applied to an n-type quantum-well IR detector (QWIPS), spectral response in the IR at temperatures as high as 150 K is observed. Measurement of the I-V characteristics, blackbody response, and noise current confirm the nature of this Schottky barrier IR detector. Work is underway to determine the mechanism for detection and to improve the device performance. Additional efforts involve the use of diffusion for mesa isolation and wavelength tuning and examination of innovative structures.

It is still a challenge to integrate the GaAs-based light-emitting devices and the well-established Si-based transistor technology. It has been our continuous effort to improve the reliability, although it remains a key concern for fabricating monolithic GaAs laser structures on Si substrates. Hybrid integration provides a promising alternative to the monolithic approach. We are studying the availability of physically attaching the readily made light-emitting devices on the Si substrates by metal bonding, as well as mounting the lifted laser thin films on the Si substrates through the aid of electrostatic force. Difference in heat dissipation through the interfaces to the substrates in various approaches will be studied and compared.

This investigation focuses on exploring the relationship between strain and phase separation in III-V semiconductors with the intention of using phase separation to achieve nanostructure devices. In situ strain can be introduced by either strain-balanced short-period superlattice technique in InGaP/GaAs and InGaAs/InP systems or by an excess incorporation of As in AlGaAs grown at low temperatures. 1-D or 2-D compositional modulation have been observed. Work is underway to realize modulation in ternary alloys by applying ex situ strain through growth of lattice mismatched cap layers. Control of modulation is of great technological importance.

The objective of this project is to develop an OEIC photoreceiver integrating a wide-bandwidth multistage I nGaAs/InP HBT-based amplifier with an InGaAs(P) p-i-n photodiode for application to 1.3 and 1.55 µm fiber-optic communication networks. The device structures are grown by gas source molecular beam and chemical beam epitaxy and utilize either C-doped or Be-doped base regions in the HBTs. The lower section (base -> ( subcollector) of the HBT structure comprises the p ⁺ -i-n photodiode structure providing both device structures are in a single growth sequence.

The goal of this project is the realization of large-scale integrated (LSI) circuits based on 50 GHz design rule InGaP/GaAs:C heterojunction bipolar transistor (HBT) technology. Device structures will be grown on GaAs wafers by MOCVD. A process for fabricating these devices on full wafers will be stabilized and statistically controlled. A user-friendly large-signal model will be developed and experimentally validated. In the final stage, an LSI-scale circuit designed at the University of Illinois will be implemented on 2- and 3-in. wafers along with circuits designed by industrial collaborators.

The objectives of this project are to develop the gas source molecular beam epitaxy (GSMBE) and chemical beam epitaxy (CBE) techniques for the growth of carbon-doped In _0.53 Ga _0.47 As and InP using CCl₄ and CBr₄ for application of these materials in high-speed heterojunction bipolar transistors (HBTs). The redistribution of carbon acceptors is compared to the redistribution of the conventional MBE acceptor species, beryllium. Hydrogen passivation of carbon acceptors and its effects on device performance as well as HBT device reliability are also investigated.

Atmospheric- and low-pressure MOCVD and gas-source molecular beam epitaxial growth techniques are used to fabricate multiple layer heterostructures in the AlGaAs/InGaAs/GaAs and InGaAsP/InP materials systems. Optical (detectors and lasers) and electronic (HBTs) devices are fabricated and characterized. Nonplanar growth and strained mismatched structures, including GaAs/Si for lasers, are studied. The impurity-induced layer disordering phenomenon is developed and characterized for laser array and other device applications suitable for optoelectronic integrated circuits. It is also being employed in conjunction with the recently discovered Al-bearing III-V native oxides, e.g., ``wet'' ambient oxidation (~400°C) of Al_xGa_1-xAs (x >= 0.5).

This project entails the growth and material characterization of high-quality InGaAs(P) layers latticed matched to InP for the development of HBTs and PINs using two novel growth techniques, GSMBE and CBE. Initial work will concentrate on the development of HBTs with a C-doped base using CCl₄ and CBr₄. Carbon is the preferred dopant for the development of high-reliability HBTs because of its low diffusivity. PIN detectors will be integrated in order to develop OEICs for 1.3 and 1.55 µm fiberoptic communication networks.

The goal of this project is to develop key technologies in areas of ultrahigh vacuum (UHV) compatible surface etching, in situ surface cleaning, and molecular beam epitaxy (MBE) regrowth of InGaAsP compounds. A UHV compatible etching technique will be used to minimize process-induced damage on patterned GaInAsP surfaces. In situ surface cleaning will be used immediately before MBE crystal overgrowth inside the growth chamber to enhance the quality of the overgrowth interface. The completion of this research should lead to new insight into innovative regrowth methods, new insight into characterization of ultrasmall heterolayers and interfaces, and improved and innovative optoelectronic and nanostructure devices.