Optical properties of tellurium-dopedInxGa1−xAsySb1−y epitaxial layers studied by photoluminescence spectroscopy

Abstract

Controlled doping of quaternary alloys ofInxGa1−xAsySb1−y with tellurium is fundamental to obtain the n-type layers needed for the development ofoptoelectronic devices based on p–n heterojunctions. InGaAsSb epitaxial layers weregrown by liquid phase epitaxy and Te doping was obtained by incorporating smallSb3Te2 pellets in the growth melt. The tellurium doping levels were in the range1016–1017 cm−3. We have used low-temperature photoluminescence (PL) spectroscopy to study theinfluence of the Te donor levels on the radiative transitions shown in the PL spectra. ThePL measurements were done by exciting the samples with the 448 nm line of an Ar ion laserwith varying excitation powers in the range from 10 to 200 mW. For the low-doped samplethe PL spectrum showed a narrow exciton-related peak centred at around 610 meV with afull width at half maximum (FWHM) of about 7 meV which is evidence of the goodcrystalline quality of the layers. For higher Te doping, the PL spectra show thepresence of band-to-band and donor-to-acceptor transitions which overlap as the Teconcentration increases. The peak of the PL band shifts to higher energies as Tedoping increases due to a band-filling effect as the Fermi level enters into theconduction band. From the peak energy of the PL spectra, and using a model thatincludes the band-filling and band-shrinkage effects due to the carriers, we haveestimated the effective carrier concentration due to doping with Te in the epilayers.