Ion Beam Assisted Quantum well Intermixing
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ABSTRACT Significant progress has been made in the past year in the use of high energy (MeV) ion irradiation to tune the bandgap and therefore emission wavelengths of single and multiple quantum well structures. These shifts are attributable to compositional mixing across the well and barrier layer interfaces, a process that is driven by the vacancy flux, released during the anneal stage, from radiation defects. We present data from a series of measurements in both GaAs- and InP-based QW structures to demonstrate the importance of the implantation parameters chosen (ion species, energy, flux, fluence and implant temperature). The dramatic difference in the response of these two systems with regard to the implant depth is believed to be associated with the very different diffusivities of the Gp III site vacancies. Prospects for implementing the irradiation approach as a spatially selective, planar process in integrated optoelectronic circuitry look very attractive and are illustrated for both passive and active components by reference to recent results from tuned wavelength lasers.
Introduction As the importance of optoelectronics to the telecommunications industry increases so does the need for the development of simple, cheap and reliable manufacturing processes for optoelectronic devices. The integration of different optoelectronic components onto a single wafer is a necessary step in achieving this goal. A significant challenge associated with integration is that of bandgap adjustment of specific components which will vary according to their individual function. For example, waveguides must have larger bandgaps than the laser producing the light they are to carry. Indeed, for lasers to be useful for WDM applications, they must be able to emit light at a range of wavelengths. Thus, to produce fully integrated optoelectronic circuits, the bandgap across a single wafer needs to be controlled in a spatially selective manner. Quantum well intermixing (QWI) is a promising technique with which these aims may be realized. Quantum wells (QW) are metastable due to the sharp concentration gradients which exist across their heterojunctions. These gradients typically vary by tens of percent over a distance of the order of 10 A and are stable at room temperature. Heating to temperatures of 1100K results in the diffusional mixing of atomic species across the interfaces [1]. The change in the associated quantum well structure, from square well towards parabolic form, lifts the energy levels so that the bandgap exhibits a blueshift [2]. Of key importance, the
815 Mat. Res. Soc. Symp. Proc. Vol. 396 1996 Materials Research Society
degree of intermixing which is induced for a specific thermal treatment is greatly enhanced by the presence of point defects within the material [3]. Amongst other techniques [3, 4, 5, 6, 7] ion implantation has emerged as a technologically viable means by which point defects can be selectively introduced to enhance QWI. Although selective bandgap engineering has been achieved with low energy (i.e.,
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