Quantum well intermixing in material systems for 1.5 μm (invited)

Abstract

Precise control over local optical and electrical characteristics across a semiconductor wafer is a fundamental requirement for the fabrication of photonic integrated circuits. Quantum well intermixing is one approach, where the band gap of a quantum well structure is modified by intermixing the well and barrier layers. Here we report recent progress in the development of intermixing techniques for long wavelength applications, discussing two basic techniques. The first is a class of laser disordering techniques which take place in the solid state. The second is a novel intermixing technique involving plasma induced damage. Both techniques enable large band gap shifts to be achieved in standard GaInAsP multiple quantum well laser structures. The potential of both techniques for photonic integration is further demonstrated by the fabrication and characterisation of extended cavity lasers.

Disordering of Quantum Structures for Optoelectronic Device Integration

“…Photoabsorption-induced disordering (PAID) (McLean et al, 1992) is an alternative laser disordering technique that makes use of the low thermal stability of the InGaAsP system. The processed material is of good optical and electrical quality, leading to the demonstration of band-gap-shifted lasers, band-gaptuned modulators, and low-loss waveguides (Marsh et al, 1998). The rapid thermal expansion results in bond breaking and lattice disruption and thus an increase of point defect densities.…”

“…Conceptually, it is simple, but its realization requires extensive growth capabilities under critical growth conditions. Also due to the fact that the thickness changes for each of the regions, it does not allow complete control of the band gap in two dimensions (Marsh et al, 1998) and the optical confinement factor is not at an optimal level in each section (Skogen et al, 2003). Another option is to vary the width of the QWs across the wafer during a single epitaxial growth (Aoki et al, 1992;Colas et al, 1991;Demeester et al, 1990).…”

Buffering Strategies for Optical Packet Switches

“…In order to engineer these three bandgaps after growth, quantum well intermixing (QWI) has been carried out to tune the bandgap in selected areas of the device chips. Using a sputtered SiO 2 technique ( Figure 6), involving the deposition of a thin film (~200nm) of sputtered SiO 2 and subsequent annealing using a rapid thermal annealer (RTA), a reliable means for obtaining post-growth shifts in the band edge of a wide range of III-V material systems can be achieved [9]. During the sputtering stage point defects are generated on the surface of the exposed semiconductor; during a subsequent anneal these point defects diffuse down through the epilayer inducing QWI, the degree of intermixing depending on the initial concentration of point defects.…”

Quantum well intermixing for photonic IC applications

“…Annealing was then applied to drive the Si into the as-grown crystal, resulting in a local mixing of the crystal layers. Quantum well intermixing in material systems for 1 .5pm has been demonstrated using laser disordering techniques and plasma induced damage [10]. The laser disordering required high power densities to melt the material, but the quality of the recrysstallized material might be poo.…”

“…The plasma process induced intermixing has been developed [10]. A new intermixing appeared particularly suitable for long wavelength applications.…”