Doping profiles of n-type GaAs layers grown on Si by the conformal method

Abstract

We study doping profiles in selectively Si-doped GaAs layers grown by the conformal method. This growth technique allows to obtain GaAs/Si with optoelectronic quality. The samples are laterally grown, and selective doping with Si is carried out in such a way that doped stripes are intercalated with undoped ones. The study of the doping profiles was carried out by cathodoluminescence (CL) and micro-Raman (pR) spectroscopy. Abrupt doping profiles between doped and undoped stripes were demonstrated by monochromatic CL images. Deep level related CL bands can be observed between 1000 and 1400 nm, evidencing the complex mechanism for Si incorporation at the growth temperature (730 'C). Net doping concentrations and mobilities across the layers were determined from the analysis of the phonon-plasmon coupled modes in the pR spectra obtained with a lateral resolution better than 1 pm.

Cathodoluminescence study of Si complex formation in self-doped and intentionally Si-doped GaAs conformal layers

“…By previous Raman and CL studies it was possible to reproduce accurately the doping profiles of the samples under study. For the ID stripe of sample M422 studied here, the free electron concentration and the free carrier mobility obtained from the Raman data were 3.7 ±0.2 ×10 18 cm −3 and 2002 ±652 cm 2 V −1 s −1 , respectively [10]. On the other hand, from the combined CL and Raman measurements, the presence of a doped stripe in ND samples has been unambiguously detected [9].…”

“…In spite of the high quality of the GaAs/Si conformal layers some detrimental features in the layers obtained by this procedure have been observed by previous Raman and CL studies, such as the existence of strain modulations [8], the appearance of a doped stripe near the seed in unintentionally doped layers [8,9] or the formation of Si-based complexes in the doped regions [10]. In particular, the presence of such complexes is expected to reduce the effective free carrier concentration, also producing a decrease of the carrier mobility, which would negatively affect the transport properties of the devices.…”

Optical Characterization of GaAs/Si Layers Grown by the Conformal Method (Confined Lateral Epitaxial Growth)

“…17 The smaller stress relieve in conformal layers compared to the one observed in the seed can be understood if one considers that the seed layer presents a high density of crystal defects, which partially relieve the stress, while the conformal layer accommodates elastically the misfit that is below the plastic limit. This should mean that the overall conformal layer is under biaxial tensile stress with respect to the seed.…”