Self-doping near the seed/layer interface in conformal GaAs layers grown on Si

Abstract

Undoped GaAs layers grown on Si substrates by the conformal method were studied by micro-Raman spectroscopy, cathodoluminescence, and diluted Sirtl solution with light ͑DSL͒ etching. The results show that nonintentional doping of conformal layers can take place near the seed/layer interface. The self-doped area presents a bright luminescence emission and shows longitudinal optic-plasmon coupled Raman modes. The nonintentional dopants were n type as deduced from Raman spectroscopy and DSL selective etching. The doped region extends only 2-3 m from the seed and was tentatively associated with enhanced diffusion of Si in the presence of dislocations at the interface between the seed and the conformal layer.

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

“…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]. This was detected for most of the conformal layers.…”

“…However, the monochromatic CL image at λ = 1000 nm, which is anticorrelated to the 840 nm one, shows clearly the presence of a bright stripe near the GaAs seed. This stripe corresponds to the above-mentioned self-doped (SD) region [9].…”

“…This was detected for most of the conformal layers. The origin of such a doped stripe was assigned to an Si contamination from the substrate in the regions nearby the seed, due to the presence of dislocations in this area, which run away 1 or 2 µm from the seed before being stopped [9]. It is interesting to observe that the free electron concentration in these regions reaches values of about 2 × 10 18 cm −3 , but moderated electron mobilities of about 900 cm 2 V −1 s −1 are reached.…”

“…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)

“…Such an observation was already reported after the investigation of the Raman shift between room temperature and 650°C. 22 This occurs whatever the direction of the luminescence fluctuations (parallel or perpendicular to the seed). The frequency shift of the LO phonon peak induced by stress is 0.391 cm −1 /kbar.…”