In-situ monitoring of AlGaAs growth with time-resolved reflectance anisotropy spectroscopy and normalized reflectance by MOCVD

摘要

AlGaAs lattice matched to GaAs substrates is a key material in vertical-cavity surface-emitting lasers (VCSELs) and edge-emitting lasers (EEL). Timeresolved re? ectance anisotropy spectroscopy (RAS) and normalized re? ectance (NR) measurements have proven their potential for the development of growth AlGaAs. In this paper, we report on the monitor and analysis of growth process of Al,Ga1-x As to optimize vertical-cavity surface-emitting lasers (VCSELs) and edge-emitting lasers (EEL) growth by using timeresolved reflectance anisotropy spectroscopy (RAS) and normalized reflectance (NR). Multi-layer AlxGa1x,As structures were grown on GaAs (001) substrates by metal-organic chemical vapor deposition (MOCVD). The NR and RAS signals at photon energy near the fundamental band gap show an oscillatory behavior during growth. We show that the different contribution of surface-induced optical anisotropy and interface-induced optical anisotropy could be distinguished in situ by RAS transient. The period of NR oscillation can be directly related to the growth rate, the error of calculated growth rate was lower than 0. 02 nm/s compared to the SEM measurement results. A significant dependence of NR and RAS signals on the aluminum compositions and surface stoichiometry at 2. OeV has been found. The first minimum of the NR oscillations of AlGaAs layers almost linearly with aluminium compositions and could be used for the determination of graded composition. Time-resolved reflectance anisotropy spectroscopy (RAS) at photon energies 2. 0 eV near the fundamental bandgap of Al0.95Ga0.05 As layer shows an oscillatory behavior during growth as shown in Fig. 1. As can clearly be seen the RAS signal difference between AlxGa1-x As and GaAs layers, this composition dependence is believed to be related to changing surface stoichiometry. Fig. 2 shows a significant dependence on the aluminium compositions in the AlxGa1-x As layers. With increasing aluminium compositions the amplitude of the Fabry Perot oscillations increase due to the higher difference of the refractive index between GaAs and AlxGa1-x As layer. Fig. 3 shows NR transients taken at 2. 0 eV during growth of lattice-matched AlGaAs for x=0, 0. 23, 0. 40, 0. 95 and linear grading from Al0.6 Gao. 4 As to pure GaAs. The first minimum of the NR oscillations of AlGaAs layers (Fig. 3) almost linearly with aluminium compositions as shown in Fig. 4, which could be used for determination of graded composition.