Investigation On The Optical Properties Of Ga_xIn_1-xP And (Al_xGa_1-x)_0.51In_0.49P Alloys

More and more attentions have been paid to the Ga_xIn_1-xP and (Al_xGa_1-x)₀.51In₀.49P alloys , which can spontaneously form ordered structure under appropriate growth conditions and which are the candidate materials for new optoelectronic devices. In this work, we applied multiple experimental methods to investigate the distinct optical properties of Ga_xIn_1-xP (x=0.52) and (Al_xGa_1-x)₀.51In₀.49P (x=0.29) alloys with CuPt-type ordered structure grown by MOVPE GaAs substrate matched.First of all. we brielly introduce the character of ordered structure and the growth parameters that influence the form of ordered structure, including growth method, growth temperature, substrate misorientation, etc. and the theoretical studies on the ordered structures. In addition, we list some distinct experimental phenomena caused by ordered structure, including band-gap reduction, blue-shift effect, valence-band splitting and band-folding effect, temperature anomaly, and so on.In the study of the ternary ordered and disordered Ga_xIn_1-xP (x=0.52) alloys, The lower emission peak, wider FWIIM and larger separation between PL and PLE spectra for ordered samples all show the great difference between ordered and disordered samples. Disordered sample is excitation-intensity-independent, while the ordered samples show excitation-intensity dependence. Both excitation-intensity dependent spectra and temperature dependent spectra, all show existence of specially separated recombination centers in ordered samples. Increasing excitation intensity or temperature, carriers transit from the disordered region to the ordered regime, leading to the intensification of the high energy peak and the blue-shift of the low energy peak. Polarized PL spectroscopy study shows no valence-band splitting in both ordered and disordered samples, the form of PL spectra, are found to be independent of the detection polarization at different excitation energy.Raman scattering spectra display superlattice effect in Ga_xIn_1-xP. Two-mode be-havior is observed: LOi (GaP-like) mode and LO2 (InP-like) mode. The FLA mode superimpose on the DALA band. In addition to the b/a ratio, we have found that the intensity of both FLA mode and LOi+LO2 mode can represent the degree of order. We also distinguish the forbidden TOi mode(GaP-like) and the splitting of LOi and LO2 mode. The appearance of TOi and the splitting of LOi and LO2 are believed to be the superlattice effect of ordering and devote together to the reduction of the "valley depth".For the quaternary (Al^Gai-Jo.siIiio^gP (x=0.29) alloys, the (Al^.Gai-Jo.siIiio^P samples show direct-band gap and a certain degree of order. The excitation-intensity independent PL spectra of ordered (Al^Gai-JosiIiin^gP alloys indicate no spatially separated centers in direct band gap (Ali:Gai_Ll.)o.5iIno 49P alloys. An anomalous blue-shift of emission peak in (Al^Gai-^o.siIikugP alloys is found for the first time by temperature-dependent PL spectra measurement. The emission peaks show Z-shape temperature-dependent behavior over the whole temperature range.PLE and polarized PL spectroscopy were applied to verify the origin of such temperature anomaly. The large separation between PL and PLE spectra, and the sub-bands of PLE spectra indicate the existence of ordered structure on the other hand. The much weaker intensity of lovv energy peak in PLE shows the origin of the temperature anomaly. At high temperature, the carriers of lovv energy band thermalize and the carriers of high energy band dominate the luminescence. The polarized PL spectra study shows no valence-band splitting but intensities differences of emission peaks ignoring the change of excitation energy and temperature. So we deduce that the band-folding elfect of superlattice effect results in the temperature anomaly.The Raman spectra of (Al^.Gai-^.Jo.giliio^gP alloys show partially three-mode behavior, double peaks of the FLA mode appears and oilers extra evidence for the band-folding effect of superlattice structure of the ordered structure. The Raman shift of GaP- and InP-like LO mode decrease and the GaP-like LO mode, the intensity of which decreases too, becomes a shoulder of the InP-like LO mode. The unresolved InP-like LO mode, GaP-like LO mode and AlP-like TO mode indicate the existence of ordered structure in quaternary (AlaGai_a:)o.5iIno.49P alloys.