Optical characterization of digital alloy In_(0.49)Ga_(0.51)P/In_(0.49)(Ga_(0.6)Al_(0.4))_(0.51)P multi-quantum-wells grown by molecular beam epitaxy

摘要

An In_(0.49)Ga_(0.51)P/In_(0.49)(Ga_(0.6)Al_(0.4))_(0.51)P multi-quantum-well (MQW) structure grown by molecular beam epitaxy using a digital alloy method was parametrically investigated by photoluminescence (PL) measurement performed in a temperature range of 10-290 K. The PL peak energies did not change with increasing temperature up to 60 K, while the PL peak energy monotonously decreased with increasing temperature beyond 60 K. From the curve fit of the linewidth full width at half maximum of the PL peak, it was observed that the homogeneous broadening of In_(0.49)Ga_(0.51)P/In_(0.49)(Ga_(0.6)Al_(0.4))_(0.51)P MQW with digital alloy barriers due to scattering by longitudinal optical phonons was smaller than that of InGaAs/InGaAlAs MQW with digital alloy barriers. This is in accordance with the existence of a relatively weak phonon-related PL peak in the PL spectrum of InGaAlP digital alloy, as compared with InGaAlAs digital alloy. The fit of the integrated PL intensity shows the occurrence of a nonradiative recombination process with an activation energy E_1=24A meV up to 60 K. On the other hand, the process of nonradiative recombination with an activation energy E_2=109 meV occurred above 60 K, which is in good agreement with one-half of the calculated total confinement energy ΔE of the electron-hole pair in the quantum well (～108 meV). The In_(0.49)Ga_(0.51)P/In_(0.49)(Ga_(0.6)Al_(0.4))_(0.51)P MQW structure with digital alloy barriers has larger activation energy (E_2= 109 meV) than In_(0.49)Ga_(0.51)P/In_(0.49)(Ga_(0.6)Al_(0.4))_(0.51)P MQW (E_2=90 meV) with analog alloy barriers. Therefore, the thermal emission of carriers into the barrier can be reduced at temperatures above 60 K due to the high effective barrier height.