Abstract
In this thesis, samples with InAs quantum dots (QD) grown on (100) GaAs substrate are investigated. AFM images exhibit the 2.4 ML InAs QDs could appear as two-group size distributions at 480 ~ 520 oC. Also observed is the large-sized relaxed islands are formed with dislocations. Besides, the two stair-like PL intensities with increasing temperature in growth rate tuning experiment is resulted from the decrease of state-filling effect of the ground state and the thermally activated repopulation of electrons to nearby dots. The calculations of band structures for quantum-well infrared photodetecotrs (QWIPs) and superlattice infrared photodetectors (SLIPs) based on time-independent Schrödinger’s equation are developed. Higher responsivity and the red shift of peak-responsivity wavelength with increased applied voltage are observed for SLIP with higher quantum-well doping. The phenomenon is attributed to the increase in the tunneling probability for low-energy photoelectrons with increasing applied voltage. To investigate the influence of QD doping densities on the performances of InAs/GaAs QDIPs, devices with different doping densities at the quantum-dot region are investigated. Higher responsivity and background limited performance (BLIP) temperature are observed for lower doping device. To reduce the operation voltages of the devices, five-stacked QDIPs with different p-type doping densities at the GaAs barrier layers are investigated. The decrease of dark currents is observed for the QDIP with 1x1016 cm-3 p-type doping density at the GaAs barrier layer, which results in an observable spectral response even for the thin five-stacked QDIP structure. With a proper choice of the p-type doping density, temperature-insensitive detectivities up to 110 K at low applied voltage 0.8 V are obtained. The phenomenon is attributed to the one order of magnitude increase of photocurrent with increasing temperature resulted from the increase of transition probability with more available empty excited states at higher temperature. Compared with QWIPs, QDIPs are of broader detection window and incident light polarization insensitive. QDIPs are of lower doping density can operate at high responsivity and high background limited performance temperature. Also observed is the decreasing photocurrent ratio of s/p–polarized lights for the QDIPs with decreasing QD doping density.