Effect of the property of dielectric capping layers on impurity-free vacancy diffusion in InGaAs/InGaAsP MQW structures

A dependence of the interdiffusion in InGaAs/InGaAsP multiple quantum well (MQW) structures on the stoichiometry of SiOx and SiNx capping layers, which were deposited with different SiH4 flow rates by plasma enhanced chemical vapor deposition (PECVD), has been studied. Decreasing the SiH4 flow rate during PECVD deposition produces relatively more voids inside SiOx or SiNx film. For both SiOx and SiNx capping layers, the blue shift of intermixed samples after rapid thermal annealing (RTA) becomes larger due to the enhancement of the interdiffusion of well/barrier caused by the increased porosity of dielectric capping layers as SiH4 flow rate decreases from 300 sccm to 20 sccm. Using SiOx (SiNx) deposited with different SiH4 flow rates, the magnitude of blue shift is varied by about 98 nm (75 nm) for the samples annealed at 850 °C for 30 s. The blue shifts of 138 nm and 98 nm of photoluminescence peak wavelength for the SiOx (deposited with 20 sccm SiH4) capped MQWs without and with an InGaAs cap layer, respectively, are observed after RTA of 850 °C for 30 s. A possible mechanism is discussed for these phenomena.