<center><b>Professor Arthur C.Gossard</head>

Professor Arthur C. Gossard

Materials Department, UCSB
Santa Barbara, CA 93106

Quantum Structure Growth, Science and Technology. New epitaxial crystal growth techniques can produce semiconductor material structures with flexibility of architecture at nearly the atomic level. These materials are redefining the realm of possibility for optical and electronic semiconductor devices and artificial quantum confinement structures [1]. U.C. Santa Barbara has three molecular beam epitaxy apparatuses and facilities that are used for research in these areas.

High Performance Graded Quantum Structures.-- This research effort has the goal of producing high-quality three-dimensional electron systems of controlled density by growth of compositionally-graded, remotely doped potential well structures. Because the electrons in these structures can move in precisely synthesized potential shapes with low damping, they can form a unique new class of solid-state electron resonators. These electron resonators are being engineered to produce Terahertz-frequency radiation [2] and to have widely tunable frequency response [3]. Among the technologies being developed for this work are growth of materials for robust, low-leakage back gates [4] and synthesis of digital alloys for precise and flexible control of composition profiles [5].

Quantum Wire and Quantum Dot Growth and Devices (jointly with Bowers and Petroff).-- We are taking several approaches to the formation of quantum wire and dot structures. In addition to growing two-dimensional electron gases in semiconductors for subsequent formation into wires and dots, we are also using special epitaxial growth techniques to form wire-like and dot-like structures directly. By using atomic terrace surface steps [6] or by making use of growth into surface grooves [7, 8], we form wire and dot quantum structures with ultra-small lateral dimensions The techniques rely on the controlled motion of atoms on surfaces. They produce lateral dimensions that can be smaller than achievable by any of the direct processing techniques. The structures are then fabricated into experimental high performance optical and electronic devices [9].

MBE Technology for Ultrafast, Ultra-high-density Optoelectronic Devices (jointly with Coldren and Bowers). -- Our objective is to develop next-generation molecular beam epitaxy technology for advanced growth and processing of optoelectronic devices. This will involve advanced in-situ monitoring and control of the molecular beam epitaxy process. Techniques to be exploited include real time measurement and control of molecular beam growth fluxes by optical absorption, control of process temperatures and film thicknesses by multiple wavelength pyrometry, and in-situ surface monitoring of growth surfaces by automated electron diffraction data collection and analysis.

Smart Optoelectronic Pixel Technology (jointly with Coldren). -- In this research, we are developing the technology for producing "smart" optoelectronic pixels that incorporate various key functions We are especially interested in optical interconnections employing light wave signal generation by surface emitting quantum well lasers, optical signal modulation by quantum well structures, and high speed optical signal detection.

Cryogenic Lasers for Low-Temperature Electronics. -- Advanced laser light sources that operate efficiently at cryogenic temperatures as low as liquid helium temperature [9] are being developed for the purpose of enabling high speed links between cryogenic or superconducting electronic circuits and room temperature electronics.

Advanced Infrared Detectors Based on Strained Layer Superlattices. -- We are developing new infrared detector technologies based on quantum wells and superlattices that are designed to overcome some of the principal limitations of the current generations of infrared detectors. By use of superlattices consisting of arsenide and antimonide semiconductor layers, we are designing and producing detector materials in which wavelengths of operation and infrared sensitivity can be engineered [10].

Selected References:

[1] "NEW QUANTUM STRUCTURES" by M. Sundaram, S.A. Chalmers, P.H. Hopkins, and A.C. Gossard, Science, 254, pp. 1326-1335 (1991).

[2] "RESONANT HARMONIC GENERATION AND DYNAMIC SCREENING IN A DOUBLE QUANTUM WELL", by J.N. Heyman, K. Craig, B. Galdrikian, M.S. Sherwin, and A.C. Gossard. Physical Review Letters, V72 N14, pp. 2183-2186 (1994).

[3] "LOGARITHMICALLY GRADED QUANTUM WELL FAR-INFRARED MODULATOR", by P.F. Hopkins, K.L. Campman, G. Bellomi, and A.C. Gossard. Applied Physics Letters, V64 N3, pp. 348-350 (1994).

[4] "THE ROLE OF MICROSTRUCTURE IN THE ELECTRICAL PROPERTIES OF GaAs GROWN AT LOW TEMPERATURE", by J.P. Ibbetson, J.S. Speck, N.X. Nguyen, and A.C. Gossard. Journal Of Electronic Materials, V22 N12, pp. 1421-1424 (1993).

[5] "BAND-GAP ENGINEERED DIGITAL ALLOY INTERFACES FOR LOWER RESISTANCE VERTICAL-CAVITY SURFACE-EMITTING LASERS", by M.G. Peters, B.J. Thibeault, D.B.Young, J.W. Scott, and A.C. Gossard. Applied Physics Letters, V63 N25, pp. 3411-3413 (1993).

[6] "TERRACE WIDTH EVOLUTION DURING STEP-FLOW GROWTH WITH MULTITERRACE ADATOM MIGRATION", by S. A. Chalmers, J. Y. Tsao, and A. C. Gossard. Journal of Applied Physics 73, pp. 7351-7357 (1993).

[7] "MORPHOLOGY AND OPTICAL PROPERTIES OF STRAINED InGaAs QUANTUM WIRES", by R. Mirin, M. Krishnamurthy, I. -H. Tan, J. E. Bowers, A. C. Gossard and E. L. Hu. J. Crystal Growth 127, pp. 881-886 (1993).

[8] "OBSERVATION OF QUASI-PERIODIC FACET FORMATION DURING HIGH TEMPERATURE GROWTH OF AlAs AND AlAs/GaAs SUPERLATTICES", by R. Mirin, M Krishnamurthy, J. Ibbetson, J. English and A. Gossard. J. Crystal Growth 127, pp. 908-912 (1993).

[9] "OPTICAL GAIN ANISOTROPY IN SERPENTINE SUPERLATTICE NANOWIRE-ARRAY LASERS", by S.Y. Hu, M.S. Miller, D.B. Young, J.C. Yi, and A.C. Gossard. Applied Physics Letters, V63 N15, pp. 2015-2017 (1993).

[10] "FAR INFRARED PHOTORESPONSE OF THE InAs/GaInSb SUPERLATTICE", by I. H. Campbell, I. Sela, B. K. Laurich, D. L. Smith, C. Bolognesi, L. Samoska, A. C. Gossard, and H. Kroemer, Applied Physics Letters 59, pp. 846-848 (1991).