Degradation of Intersubband Transitions in Electron Irradiated GaAs/AlGaAs Multiple Quantum Wells With Superlattice Barr
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Intersubband transitions in Ill-V semiconductor multiple quantum wells remain a focus in optoelectronics research since they form the basis for many devices, including long wavelength, quantum well infrared photodetectors (QWIPs).' The studies done over the last 20 years characterizing the intersubband transitions in MQW structures have led to the development of high uniformity QWIP focal plane arrays. Of the work on intersubband transitions in MQWs, little has focused on the effects of electron irradiation. The role of QWIPs for space-based remote sensing and surveillance has prompted interest in studying the survivability and radiation hardness of multiple quantum well structures in the space environment. In this study, an optical characterization of the effects of electron irradiation on the intersubband transitions in n-type GaAs/ Al.4Ga.6As multiple quantum wells with superlattice barriers was done using the optical absorption technique. The recent studies on irradiation effects on interband and intersubband transitions in multiple quantum well structures have focused on two primary effects: 1) degradation of the intersubband transition and 2) shifting of the intersubband and interband transition peak position energy. Degradation of the intersubband transition by electron irradiation was initially reported by Manasreh et. al., who observed it in the absorption spectra of InGaAs/AlGaAs MQWs irradiated with 2 MeV electrons. 2 A complementary study on the effects of 1 MeV proton irradiation of GaAs/AlGaAs MQWs showed complete degradation of the intersubband transition to occur at relatively lower doses (- 1014 cm 2), in comparison with the electron irradiation 503 Mat. Res. Soc. Symp. Proc. Vol. 607 0 2000 Materials Research Society
(- 10'7cm 2).3
This study also demonstrated that intersubband transitions in MQW structures with super lattice barriers degrade at a faster rate than structures with "bulk" barriers. A recent investigation by Tan et. al. of the shifting of the peak position energy in GaAs QWs by proton irradiation/ annealing has demonstrated a linear relationship between wavelength shift and irradiation dose.4 Gamma ray irradiation of InGaAs/AlGaAs MQWs has also been investigated.5 In this report, the relation between the electron irradiation dose and the absorption intensity of the intersubband transitions is examined for GaAs/Al. 4Ga.6As MQWs with superlattice barriers. Degradation and enhancement of particular intersubband transitions are observed after electron irradiation. The intensity of the transition between the ground and first excited states at 77 K is found to decrease exponentially with irradiation dose. This effect can explained in terms of the trapping of the two dimensional electron gas in the quantum well by the irradiation induced defects. In comparison, the intensity of the transition between the ground state and the higher energy miniband at 295 K is observed to grow exponentially with irradiation dose. It is suggested that this is due to mixing of the quantum wells and superlat
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