無摻雜GaAs/AlGaAs量子井之橫向p-i-n二極體

Abstract

在表面聲波(SAW)驅動的單光子源元件中，高品質的二維p-i-n接面是個關鍵的因素。另外二維p-n橫向接面是另一個在光學方式探討二維系統中電子自旋有競爭力的選擇。在本論文中，我們發展了一個利用普通的金屬化與曝光製程，可靠且相對簡單的方式，在完全沒有摻雜的GaAs/AlGaAs 量子井結構上來製作p-i-n橫向接面。 一個沒有摻雜的異質接面所誘發出的二維電子或電洞氣相較於有摻雜的系統表現出許多的優點，例如遷移率，特別是在低載子濃度下。為了得到這個優點，我們發展了一個可被誘發的橫向接面二維 p-i-n二極體。兩種不同類型的通道透過金屬-絕緣質-半導體(MIS)閘極，其稱之為單一閘極元件誘發出。在p類型施加負電壓與n類型施加正電壓下，2DHG與2DEG通道可以在GaAs量子井中被誘發出，所以一個橫向接面的二維 p-i-n二極體因此產生。我們研究了這個元件在低溫的電性與光性。此2DEG與2DHG被誘發的臨界電壓分別為 3.5V與 -1.25V。元件的電壓電流曲線在導通電壓1.53V電壓時呈現了清楚的整流特性。及符合理論的計算導通電壓值 Vbi = 1.535 V。電激發螢光的峰值在1.529 eV (811 nm)而半高寬有4.4 meV。這吻合理論計算中量子井基態的能量。 然而因為閘極與通道的距離使得閘極控制量子井的載子能力並不是非常有效率。導致兩個在絕緣層上的上層閘極不能彼此靠得太近。這直接影響到在i區域的載子複合。另外這個限制讓元件的發展上更加受限，例如表面聲波驅動的單光子源。因此我更發展了兩個通道同時有表面閘極與上層閘極的雙閘極結構。這個表面的蕭基閘極提供了一個通道中載子很好的控制能力下同時可以彼此靠近。跨越源極與汲極在絕緣層這上的上層閘極，可以在歐姆接觸與閘極間，沒有漏電路徑下控制著源極與汲極間的通道載子。雙閘極元件表現出較穩定的電性與清楚的光學頻譜。這些成果展示出這個元件非常適合在單光子元件的應用。

In SAW-driven single-photon source devices, the key component is a high-quality 2-D p-i-n junction. In addition, lateral 2-D p-n junctions are also potential candidates for investigating the properties of electron spins in low-dimensional systems by optical methods. In this thesis, we developed a reliable and relatively easy method to fabricate a lateral p–i–n junction in a completely undoped GaAs/AlGaAs quantum well structure by utilizing conventional metallization and lithography processes. An induced gas (2DEG or 2DHG) in undoped heterostructure shows great advantages compared to a doped gas, such as high mobility, especially in low carrier density. To gain the advantage of induced gas, we developed an induced lateral 2D p-i-n diode. The two different types of channels are induced via metal-insulator-semiconductor (MIS) gates, which called single-gate devices. With a negative voltage applied on the p-gates and a positive voltage applied on the n-gates, both 2DHG and 2DEG channels can be induced in the GaAs quantum well, so a lateral 2-D p-i-n diode is formed. The electrical and optical of the devices at low temperature are studied. The 2DEG and 2DHG can be induced at threshold voltage of 3.5 V and -1.25 V, respectively. The current-voltage curve of the devices shows clearly the rectifying behavior with a turn-on voltage of 1.53 V. This is in agreement with the theoretical calculation of the built-in voltage Vbi = 1.535 V. The main peak of electroluminescence is at 1.529 eV (811 nm) with the full-width at half-maximum of 4.4 meV. This is in good agreement with theoretical calculation of ground state energy of the quantum well. However, the gate control of the carriers in the quantum well is not very efficient because of the distant gate from the channel. As a result, the two top gates on the insulator could not be put too close to each other. This directly affects the carrier recombination in the i region. In addition, this limits further development more complicated devices, such as SAW-driven single-photon source. Thus, we developed the twin-gate structure which has surface gate and top gate for each channel. The surface Schottky gates provide a very good control for the carriers in the channel and at the same time can be put very close to each other. The top gates, which overlap the source and the drain through the insulator spacer, control the carriers in the channel regions next to the source and the drain without having a leakage path between the gates and the ohmic contacts. The twin-gate devices show more stable electrical characteristics and clearer optical spectrum. These results demonstrate that the device is promising for applications in the single-photon devices.