Cathodoluminescence study of laser recrystallized CdTe layers

Abstract

CdTe͑100͒/GaAs͑100͒ and CdTe͑111͒/CdTe͑111͒ layers grown by metalorganic vapor phase epitaxy ͑MOVPE͒ were investigated. The layers were recrystallized to improve their morphology by scanning the surface with a 100 m diameter spot from an Ar ion laser beam ( ϭ514.4 nm). Cathodoluminescence spectra from both as-grown and recrystallized CdTe MOVPE layers are used to monitor the effect of the recrystallization procedure. The laser recrystallization results in important changes on the spectral distribution of luminescence. Deep-level bands associated to different defects are shown to be very sensitive to the laser recrystallization procedure. The effect of the different substrates on the defect structure of the layers is also related to the changes observed in the cathodoluminescence spectra. © 1997 American Institute of Physics. ͓S0003-6951͑97͒01947-5͔Metalorganic vapor phase epitaxy ͑MOVPE͒ is a technique commonly used to grow CdTe layers on different lattice mismatched substrates like Si, GaAs, sapphire, etc. 1 These layers are used as substrates for subsequent epitaxial growth of Hg 1Ϫx Cd x Te layers for infrared applications ͑for recent examples, see Refs. 2-5͒. It is widely accepted that the properties of CdTe MOVPE layers are strongly dependent on several technological factors, among which the substrate nature is one of the most important. 6 In particular, previous studies of CdTe/sapphire and CdTe/GaAs layers grown by a low-temperature MOVPE have shown that the as-grown layers have a low quality, rough surface due to strain raised from the large lattice mismatch. [6][7][8] To overcome this problem, postgrowth laser recrystallization has been recently proposed as a method to improve the surface morphology of CdTe MOVPE layers. 8 Nevertheless, it is still an open question how the laser recrystallization procedure affects other properties of the layers besides surface morphology.Cathodoluminescence ͑CL͒ microscopy has been shown to be a very useful tool to characterize CdTe bulk crystals submitted to different technological treatments like thermal annealing, 9-11 doping, 12 or epitaxial overgrowth. 13 The capability to obtain both spectral and spatial resolution allows us to gain quite valuable information about the defect structure of the material. Though bulk crystals have been extensively studied by luminescence techniques, not so much work has been done to characterize CdTe epitaxial layers. In this letter, we report the results on cathodoluminescence studies of asgrown and laser recrystallized CdTe/GaAs and CdTe/CdTe MOVPE layers and show the effect of the laser recrystallization on the radiative defects contributing to the CL emission of the layers. The influence of the substrate on the behavior of the epilayers under laser irradiation is also reported.The samples investigated were CdTe͑100͒ and CdTe͑111͒ layers grown on GaAs͑100͒ and CdTe͑111͒ substrates by MOVPE. The layer thicknesses were in the range 4-10 m. The MOVPE growth was carried out at 340°C for 3-5 h using dimethylcadmium and diisopropiyl tel...

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