| Summary: | 博士 === 國立臺灣大學 === 電機工程學研究所 === 90 === In this thesis, samples with InAs quantum dots (QD) grown on (100) GaAs substrate by molecular beam epitaxy (MBE) are investigated. The more uniform InAs QDs is observed for samples grown under As shutter closed conditions. Also observed is the formation of two-group size distribution of QDs with increasing substrate temperature. The state filling effect with increasing laser pumping power and the redistribution of electrons in the InAs QDs to nearby dots with increasing temperature is observed via photoluminescence measurements. The effect of high-bandgap blocking layers on the performances of superlattice infrared photodetectors (SLIPs) is investigated. The improvements of responsivity and the voltage asymmetry response are observed for SLIPs with different device structures. The red shift of spectral responses of SLIPs is attributed to the reduction of absorption coefficient at the zone center of the SL structure. Grown under As shutter closed condition, ten-stacked InAs/GaAs quantum-dot infrared photodetectors (QDIPs) with different device parameters are investigated. Negative differential conductance (NDC) observed for QDIPs without (AlGa)As blocking layers is attributed to the intervalley scattering induced by the local high field domain in the QD structure. The depression of both photocurrent and dark current and the invariant Fermi level are observed for QDIPs with two (AlGa)As blocking layers at either side of the QD structure. The enhancement of responsivity is achieved for QDIPs with single-sided (AlGa)As blocking layer. Also observed is the depression of dark currents under this structure such that high-temperature operation up to 175 K is demonstrated. Although unclear yet, certain devices with (AlGa)As blocking layers at each side of the QD structure have revealed near-room-temperature operation of PV response. Compared with SLIPs, QDIPs are of higher peak responsivity, broader detection window and incident light polarization insensitive. And the increase of photocurrent of QDIPs with increasing temperature is observed while the invariance of photocurrent is observed for SLIP.
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