砷化銦鎵量子點/環紅外線偵測器之磊晶成長製作及其特性之研究

The Epitaxial Growth and Optoelectronic Properties of In(Ga)As Quantum Dot/ Ring Infrared Photodetectors

李政暵(Jheng-Han Lee)

指導教授 ： 李嗣涔

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.10067

摘要

在此篇論文研究中，藉由原子力顯微鏡、掃描式電子束顯微鏡以及光激發系統來研究砷化銦量子點以及砷化銦鎵量子環的光學特性及表面形貌。為了在分子束磊晶機台中得到比較好的成長條件，像是成長溫度、五族氣體流量等許多不同的參數將在此論文中進行探討。之後將以最佳化的參數對於量子點以及量子環紅外線偵測器進行成長。此外，在這篇論文中另一個主要的目的就是改善紅外線偵測器元件的特性，像是響應值、操作溫度等。為了達成特性改善的目的並且不讓元件的結構變得複雜化的前提之下，我們提出以表面電漿結合量子點紅外線偵測器、氨氣的電漿處理、以及矽摻雜的量子井插入層來進行元件特性的探討。其中表面電漿結合量子點紅外線偵測器除了讓響應特性改善之外更可以作為特定波長偵測之用，可使得焦平面陣列紅外線偵測器的整合較為簡單。利用氨氣的電漿處理則是可以消除由於製程或是自然氧化下所產生的缺陷，這些缺陷會使得元件的暗電流較原先來的高，但在經過電漿處理後，元件的暗電流平均可以下降10到100倍，如此可以用來提升元件的特性，包含響應以及操作溫度等。然而由於暗電流仍舊會隨著溫度而快速的上升，所以光是依靠製程上面降低暗電流並無法大幅提升操作溫度，於是利用量子井作為額外的載子補充層的紅外線偵測器在此論文中被提出並進行研究，傳統上的光載子的訊號主要是從兩端有矽摻雜的電流接觸端所貢獻，但對於離其較遠的內部量子點而言，此種填充的效率並不高。於是乎把輕微摻雜矽的量子井放中原先結構中間最作為載子補充層既可不複雜元件結構又可以大幅提升元件的操作溫度至230K。對於此種利用量子井作為載子補充層的結構，我們也利用模擬、光暗電流以及穿透式電子顯微鏡的分析來架構其高溫操作的理論雛型。最後，利用量子環結構，也成功的將偵測較微小能量的兆赫偵測器給製造出來。其可偵測的頻率為1.7兆赫，即為波長175微米左右的能量。

關鍵字

量子點 ； 量子環 ； 紅外線偵測器

並列摘要

The Growth mechanism of the In(Ga)As quantum dots (QDs) and rings (QRs) are investigated by the atomic force microscopy, scanning electron microscopy and
photoluminescence (PL). Different growth conditions are studied to obtain homogenous QDs and QRs. The uniformity is important especially for quantum dot (QDIPs) and quantum ring infrared photodetectors (QRIPs). For infrared photodetectors, two-color or multi-color, high temperature operation and long wavelength (Terahertz) detection must be achieved to have high performance in responsivity and detectivity. In order to achieve the goals, the surface plasmon combined with QDIP, NH3 plasma treatment passivation, the well in quantum dot stack (WD) structure and QR structures are adopted.
The two-color QDIPs are fabricated successfully by the use of top metal contact perforated with the cross metal hole arrays. The periodic contact metal hole arrays play double roles, i.e., the top contact and the optical filter. Patterning with lattice constants a = 1.6 μm and a= 2.8 μm, the 4-6 μm and 8-12 μm wavelength ranges can be detected. Its detectivity can be increased up to 1.85 × 1011 cmHz1/2/W at 20 K and the background limited temperature (BLIP) is between 60-70 K. It can be applied to fabricate the focal plane array (FPA)
To achieve high-temperature operation, the performance of AlGaAs/GaAs QWIP and InAs/GaAs QDIP with and without NH3 plasma treatment are investigated. It is demonstrated that the NH3 plasma treatment not only gets rid of the oxide defects such as Ga2O3, As2O3 and As2O5, but also prevents the formation of oxides on the GaAs surface when exposed to atmosphere for one month. It lowers the dark current of QWIP and QDIP. The peak responsivity of the QWIPs without NH3 plasma treatment is 0.48 A/W, and the detectivity is 3.13 × 109 cm-Hz1/2/ W at 1.5 V, and 60 K. However, the QWIP after the 10 minute NH3 plasma treatment exhibits a better performance. The highest operation temperature can be increased from 60 to 90 K. At 90 K, the peak responsivity of the NH3 treated QWIP is 1.25 A/W and the detectivity is 3.54 × 109 cm-Hz1/2/ W at 1.5 V. Similarly, the responsivity of the NH3 plasma treated QDIP enhances from 0.8 to 1.5 A/W at 10 K and from 0.06 to 0.09 A/W at 90 K under the bias of ± 1.5 V and 0.8 V, respectively. The operation temperature also increases from 90 to 140 K. It states the importance of passivation to enhance the device performance.
Instead of lowering the dark current, a simple structure of WD-QDIP is proposed which can be operated at a high temperature (~230 K) easily. In traditional QDIPs, the carriers (electrons) are supplied from the top and bottom contacts. In order to achieve high temperature operation, various methods are applied to reduce the dark current. This new design adopts the opposite concept, a QW layer doped with Si to 1017/cm3 is inserted in the middle of a stack of 10 QDs layers to serves as a carrier injection layer to supply carriers to QDs layers quickly and sufficiently. The dark current is increased significantly, however, the photo current (PC) is increased even more. Therefore, the operation temperature can be raised to 230 K. This WD-QDIP achieves a responsivity of 0.046 A/W and the detectivity of 1.26 x 107 cmHz1/2/W under the bias of 0.4 V at 230 K.
In addition, the carrier transportation mechanism in this WD-QDIP is studied to reveal the existence of two-channel system, the photovoltaic effect and the presence of the scattered electrons. These phenomena describe and prove how a WD-QDIP can be operated at high temperatures. In these discussion, the scattered QDs and the density of QDs are regarded as the key factors to high-temperature operations.
For terahertz detection, an InAs/GaAs quantum ring infrared photodetector (QRIP) has been fabricated successfully. This photodetector demonstrates a cutoff wavelength at 175 μm (1.7 THz) and the detectivity of 1.3×107 cmHz1/2/W at 80 K under the bias of 80 mV. The precise control of the In(Ga)As ring height by capping GaAs layer thickness is responsible for extension of the detector response to terahertz range.

並列關鍵字

Quantum Dot ； Quantum Ring ； Infrared Photodetector

參考文獻

3. J. Tersoff and F. K. LeGoues Phys. Rev. Lett., 72, 3570–3573, (1994).

8. Fafard, Photonics Spectra 31, 160 (1997).

9. R. Mirin, A. Gossard, and J. Bowers, Electronics Lett. 32, 1732 (1996).

15. D. G. Deppe and H. Huang, Appl. Phys. Lett., 75, 3455 (1999).

24. S. F. Tang, C. D. Chiang, P. K. Weng, Y. T. Gau, J. J. Luo, S. T. Yang, C. C. Shih, S. Y. Lin and S. C. Lee, IEEE Photonics Technology Letter, 18, 986-988, (2006).