InAs/InGaAs量子點光電容特性

Abstract

本論文是利用MBE系統成長的砷化銦(2.34 ML)的量子點樣品與應力鬆弛方式(3.3 ML)的量子點樣品比較，並透過光性與電性量測分析來瞭解其樣品的光電特性，接著透過光激發下的電性量測觀察樣品中的光電特性。第一部分：藉由光性與電性量測，包括螢光頻譜(Photoluminescence, PL)、電容電壓量測(Capacitance-Voltage, C-V)、深層能階暫態頻譜儀(Deep Level Transient Spectroscopy, DLTS)、穿透式電子顯微鏡(Transmission Electron Microscope, TEM)的量測，來探討砷化銦/砷化鎵量子點結構中其量子能階、缺陷能階分佈以及電子放射機制。第二部分：由DLTS 量測分析上發現缺陷的電子放射速率會受到電壓掃動速度影響。因此改變不同掃動速度的C-V量測，可以發現樣品在高溫下的確出現電容值變化並將該結果與應力鬆弛的樣品做比較，說明了未應力鬆弛的樣品中確實存在一個相當深的缺陷是DLTS難以完整量測。第三部分：將兩片樣品在光激發下，並改變光源能量作電容電壓量測，分析其光電容特性。光電容變化分為三個區域，分別為EL2缺陷、PL光譜、深層能階缺陷所造成。而兩樣品的光電容有極大差距是由於應力鬆弛下量子點與砷化鎵之間的銦與鎵交換抑制了EL2缺陷的形成造成EL2缺陷濃度降低。另外，藉由不同的雷射光源激發未應力鬆弛砷化銦量子點樣品作PL量測可以確立深層能階缺陷訊號出現於特定激發光源下。最後選用特定激發光源為樣品做C-V量測可以確定在低能量(0.8 eV)雷射光下確實能激發出EL2缺陷能階中的電子貢獻在光電容上，將雷射光能量提高至1.17 eV後照射樣品，則激發了量子點能階中的電子貢獻PL光譜上，並且由縱深圖上的變化分析載子被激發後的躍遷情形。

Electrical and optical properties for relaxation and non-relaxation InAs quantum dots (QDs) with an InGaAs capping layer fabricated by molecular beam epitaxy (MBE) deposition, were studied. First, the properties of quantum states, defect states, and mechanism of electron emission in InAs QDs samples are studied by using capacitance-voltage (C-V) profiling, bias-dependent deep level transient spectroscopy (DLTS), transmission electron microscope (TEM), and photoluminescence (PL) measurements. Second, the bias-dependent sweeping rate affects electron emission from the defect state by DLTS spectra. An elevated capacitance is found at the temperature of 300K by C-V measurement with the variation of sweeping rate, suggesting a non-relaxation InAs QDs containing a deep defect. Third, the photo-capacitances for relaxation and non-relaxation InAs QDs are investigated by using C-V measurement under illumination with the variation of energy (0.7 ~ 1.56 eV). The three regions are considered the electron emission from the EL2 defect state and the deep defect state and carrier recombination in the energy-dependent photo-capacitance spectra for non-relaxation InAs QDs. The large difference of photo-capacitance for two samples is due to the concentration of EL2 defect states, suggesting the inter-diffusion with In and Ga atoms suppress the EL2 defect forming in the relaxation InAs QDs. In addition, an existence of the deep defect is confirmed in the PL spectra by using an excitation energy-dependent laser. By illumination energy of 0.8 eV, photo-capacitance originates from the electron emission of EL2 defect states, and the valley peak shift can analyze the mechanism of excess electrons emission from EL2 defect states in the carrier distribution profiling. As illumination energy is 1.17 eV, the recombination rate of excess carriers increases accompanying photo-capacitance decreases.