砷化鎵系列量子點與量子井紅外線偵測器之研究

The Study of GaAs-Base Quantum-Dot and Quantum-Well Infrared Photodetectors

周淑婷(Shu-Ting Chou)

指導教授 ： 吳孟奇

國立清華大學/電機資訊學院/電子工程研究所/博士(2006年)

https://doi.org/10.6843/NTHU.2006.00696

摘要

在本論文中，我們在(100)指向的砷化鎵基板上成長砷化銦量子點結構。由原子力顯微鏡圖像顯示長晶溫度在480~520 ℃時，2.4單一層砷化銦量子點的尺寸呈現了兩種不同的分佈，同時我們也發現體積較大的量子點和缺陷有關。而改變磊晶速率的實驗中，光激發螢光強度對量測溫度的非線性變化可能是因為量子點中基態的填態效應減小所致。我們利用薛丁格方程式來模擬量子井和超晶格紅外線偵測器能帶結構的理論計算。此外，我們觀測到較高量子井掺雜密度的超晶格紅外線偵測器隨著偏壓的增加，有較高光響應度和頻譜響應紅位移的現象，此一現象是導因於低能量的光電子穿遂機率增加所致。針對量子點掺雜密度的研究，我們成長了不同掺雜密度的砷化銦/砷化鎵量子點紅外線偵測器結構，我們觀測到低掺雜密度的元件有較高的光響應度和背景限制溫度。為了降低元件的操作偏壓，我們利用不同的p型掺雜密度的砷化鎵緩衝層成長五層砷化銦/砷化鎵紅量子點外線偵測器結構，我們觀察到掺雜密度1 x 1016 cm-3的p型砷化鎵緩衝層暗電流減少，此一結果使得只有五層的紅量子點外線偵測器結構也可觀察到光響應度。因此，當選擇適當p型掺雜密度的砷化鎵緩衝層，我們在低偏壓0.8伏特觀察到110 K與溫度不靈敏偵測度的現象，此一結果是在高溫下有更多有效空激發能階使得躍遷機率增加，故此現象是導因於隨著溫度增加光電流劇增所致。與量子井紅外線偵測器相比較，量子點紅外線偵測器具有較寬的偵測波段以及可吸收正面入射光的特性。低掺雜密度的量子點紅外線偵測器有較高的光響應度和背景限制溫度，我們也觀察到隨著量子點掺雜密度減少，s/p偏極光的光電流比減少的特性。

關鍵字

量子點紅外線偵測器 ； 量子井紅外線偵測器 ； 超晶格紅外線偵測器 ； 砷化銦/砷化鎵 ； 砷化鎵鋁/砷化鎵 ； 暗電流 ； 光響應度 ； 偵測度 ； 量子點

並列摘要

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.

並列關鍵字

Quantum dot infrared photodetector (QDIP) ； Quantum well infrared photodetector (QWIP) ； Superlattice infrared photodetector (SLIP) ； InAs/GaAs ； AlGaAs/GaAs ； dark current ； spectral responsivity ； detectivity ； Quantum dot

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