QUANTUM WELL INTERMIXING IN InGaAsP/InP LASERS USING LT-lnP

Abstract

This thesis presents quantum well intermixing in InGaAsP/lnP quantum well laser structures using a low temperature grown InP (LT-lnP) cap. The thermal response of the underlying semiconductor material was examined as a function of rapid thermal anneal temperature and time and is also studied with respect to structure thickness, surface composition (InGaAs or InP), choice of p or n-type InP substrate and doping within the structure, and changes in growth temperature of the active region. It was found that structures with Be-doped cladding exhibit large enhanced intermixing through the possible dissociation of a grown-in defect complex. It was also found that a process, with an onset of -690°C, becomes the dominant mechanism for intermixing in both full and partial laser structures at temperatures >750°C when the samples are annealed for 60 sec. It is proposed that this blueshift is the combination of another defect complex that dissociates at anneal temperatures £750°C to produce a fast diffusing defect that can enhance intermixing within <8 sec, and also group V vacancy diffusion that originates from the desorption of group V species from the samples’ surface at high anneal temperatures and long times. Intermixing was also studied as a function of the growth parameters of the LT-lnP caps grown by GSMBE. It is shown that at temperatures below congruent sublimation for InP (360°C), P|n antisite defects are incorporated as a result of

iv non-stoichiometric growth. These defects are incorporated with decreasing growth temperature and also with increasing phosphine flow. The results will show that the rate of intermixing increases with increasing defect incorporation, and that the intermixing is not exhibited in samples with the LT-lnP cap removed prior to annealing. Furthermore, the intermixing is seen to occur for anneal temperatures >640°C. Therefore, it is suggested that at this temperature there is sufficient thermal energy forthe P|n antisite to dissociate into a P interstitial and In vacancy. The P interstitials are highly mobile in InP and subsequently diffuse rapidly to produce large blueshifts within <15 sec.