利用石墨烯及光柵結構增益量子井超晶格感測器之響應度

Abstract

本實驗室長期發展量子井紅外線偵測器之技術，透過量子井以及超晶格兩種磊晶結構之組合，元件得以同時享有低偏壓的工作區段，以及多段波長的光偵測特性。透過改變偏壓大小，能夠調控元件偵測之波段，在不同的量測狀況下可以自由改變偵測模式，增加量測時的彈性。 量子井紅外線偵測器因極化選擇的問題，無法有效吸收正向入射之光線，使得其訊號強度不佳。而本研究透過覆蓋石墨烯以及製作光柵結構的方式，改善正向入社效率不佳的問題。透過石墨烯和砷化鎵產生之異質接面，在元件中形成內建電場，分離因吸收光能量而激發之載子，生成光電流。此接面將能夠代替主動層吸收正向入社的光線，並且經由量子井區域以及超晶格區域進行過濾，形成具有量子井及超晶格偵測頻譜的光訊號，有效改善因正向入射光吸收不足，而導致光電流低落之問題。並且透過接面處空乏區與主動層區域之重疊，更進一步地增加元件萃取電子的能力。而光柵結構則是改變入射光的行進方向，以漸逝波的方式聚集在光柵結構處。光行進方向之改變將導致其電場方向改變，使其得以被給主動層吸收。由於在製作光柵結構的過程中，將大部分元件之半導體區域蝕刻掉，此方式不僅增加了元件的光電流，還大幅降低暗電流，使得元件之偵測度有顯著的提升。 在本篇研究中，元件經石墨烯覆蓋以及光柵結構的製作後，其偵測光訊號之能力，各項指標性的元件參數，皆有大幅度的提升。響應度提升了10倍之多，暗電流下降了十倍左有，而偵測度提升了近50倍。偵測溫度也得到大幅的提升。在改良元件以後，此元件得以在163K之環境溫度下進行光訊號的偵測，和元件經過處理前之量測溫度100K相比，相差了約40K左右。

Our team has developed the technology of quantum well infrared detectors. Through the combination of quantum wells and superlattice structures, the devices have low-bias working sections and multi-mode wavelength detection characteristics. By changing the bias voltage, the wavelength detection can be adjusted, and the detection mode can be changed under different conditions to increase the elasticity during measurement. Due to the problem of polarization selection, the quantum well infrared detector cannot effectively absorb the normal incident light, which makes the signal quality poor. In this study, the problem of poor absorption of normal incident light has been improved by covering graphene and fabricating the grating structure. A heterojunction generated by graphene and gallium arsenide forms a built-in potential in the device, and separates the carrier excited by the absorbed light energy to generate photocurrent. This junction will replace the active layer to absorb the normal incident light, and then filter through the quantum well region and the superlattice region to form an optical signal with quantum well and superlattice detection spectrum. Through the overlap of the depletion zone and the active layer zone at the junction, the ability of extracting electrons was further increased. The grating structure changes the direction of the incident light and focus the light at the grating structure in an evanescent manner. A change in the direction of the light will cause its electric field direction to change, allowing it to be absorbed by the active layer. Since a huge parts of semiconductor region is etched away during the fabrication of the grating structure, this method not only increases the photocurrent of the component, but also greatly reduces the dark current, so that the detectivity of is significantly improved. In this study, after the devices are covered by graphene and the grating structure is fabricated, the ability to detect optical signals and the various parameters are greatly improved. The responsivity has increased by a factor of 10, the dark current has dropped by a factor of 10, the detectivity has increased by nearly 50 times. The detection temperature has also been greatly improved. After the device is improved, it can detect the optical signal at the temperature of 163 K, which is about 40 K different from the measured temperature of 100 K before the component is processed.