Vacancy Promoted Interdiffusion in Quantum Wells and Applications to Optoelectronic Devices
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VACANCY PROMOTED INTERDIFFUSION IN QUANTUM WELLS AND APPLICATIONS TO OPTOELECTRONIC DEVICES M. GHISONI*, A.W. RIVERS*, K. LEE*, G. PARRY*, X. ZHANG**, A. STATONBEVAN**, M. PATE*, G. HILL*, C. BUTTON AND J.S. ROBERTS***. * University of London Interdisciplinary Research Centre for Semiconductor Materials, Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, U.K. ** University of London Interdisciplinary Research Centre for Semiconductor Materials, Department of Materials, Imperial College of Science Technology and Medicine, London SW7 2BP, U.K. ***SERC Central Facility for III-V Materials, University of Sheffield, Sheffield S1 3JD, U.K. ABSTRACT In this paper we shall look at a technique, known as impurity free vacancy diffusion (IFVD) for selectively altering the optoelectronic response of quantum well material after growth with a view to monolithic device integration. We will discuss the mechanism, practical considerations and some possible applications.
INTRODUCTION The last decade has seen a rapid advance in optoelectronic devices based on quantum well (QW) material [1, 2]. However true commercial viability will only come with the development of successful monolithic integration, be that optoelectronic integrated curcuits (OEIC) [3, 4] where optical components are combined with electronic circuitry, or photonic integrated circuits (PIC) [5] where the predominant devices are optical. The need for devices performing different functions means that for an epitaxially uniform layer trade-offs must exist, thus the ability to produce integrated devices having differing optical responses is desirable. This has led to extensive studies and advances in selective epitaxial growth [6, 7] and re-growth technology. The technique we shall be discussing in this paper, is impurity free vacancy diffusion (IFVD), which in contrast is a postgrowth process and involves the selective modification of the epitaxial layers. The technique of IFVD is similar to the much more extensively studied impurity induced layer disordering (IILD) where implantation or diffusion of ions/atoms followed by annealing is used to cause the selective intermixing of the QW layers into the equivalent AlGaAs alloy (in this paper we shall limit our discussions to the GaAs/AlGaAs system) [8, 9]. The alloy having a higher bandgap energy (i.e. shorter wavelength) and lower refractive index than the QW system has allowed IILD to be used to produce passive waveguiding sections [10], and provide lateral confinement for buried heterostructure lasers [11]. IFVD also causes a blue shift in the spectra, but the intermixing is not so severe as to Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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produce an alloy but rather modification of the well shape occurs, resulting in retention of the QW characteristics. The existence of excitonic features and the spectral response to an applied field, namely the quantum confined Stark effect (QCSE) [12], after intermixing means that these areas can still be us
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