臺灣博碩士論文加值系統

在紅外線偵測器的研究領域中，我們朝向製作出偵測波長範圍大和高響應的元件，所以我們改變之前的結構想去得到更好的響應。

在這篇論文當中，我們研究了兩個不同的樣品(S1和S2)，所有樣品的結構都包含了兩個超晶格結構並且再中間夾了一個電流阻擋層。其中一個偵測器S1包含了一個50nm的電流阻擋層並且在超晶格結構中均勻摻雜。另一個偵測器S2包含了300nm的電流阻擋層和兩個間接摻雜的超晶格結構(每三個量子井只在中間那一個有摻雜)。我們可以透過改變偏壓的極性去切換兩個不同的超晶格結構。

首先，我們討論超晶格結構週期數的影響，因為3週期結構的群速大於15週期的群速，所以在低偏壓時的響應3週期會大於15週期。接著我們討論摻雜方式和電流阻擋層的影響，我們可以發現不同摻雜方式的波長響應也會有很大的不同，因為不同的摻雜會有不同的Fermi level而影響了我們原本所設計的能階，然後我們比較電流對電壓的圖形，可以發現厚的電流阻擋層不僅會降低暗電流，同時也會使的光電流和光響應降低，所以厚的電流阻擋層與薄的電流阻擋層的偵測率皆在同一個倍率。

The domain of superlattice investigation, we want to produce the larger wavelength range and higher photoresponse. Then, we change the structure to get the better responsivity.
In this thesis, we investigated the two samples S1 and S2. Both samples contain a current blocking layer embedded between two superlattice with different period numbers. One of the detectors called S1 contains 50nm blocking barrier and doped in every well in superlattice. The other called S2 contains 300nm blocking barrier and only doped in the middle period of each three periods in superlattice. We can switch the spectral response between two superlattice by changing the voltage polarities.
The first discussion is about the effect of period number. We observed the responsivity of 3-period superlattice is larger than 15-period one in the low bias. This is due to the electron group velocity of 3-period in the second miniband is larger than 15-period. Then, we discuss the effect of the different doped method and the different blocking barrier thickness. We find that the doped method will change the photoresponse shape. The selective doped method has different peak with the uniformly doped layers. Because the different doping density has different Fermi level to affect our design energy band states. We have compared the current curve. The thick blocking barrier will not only reduce the dark current but also the responsivity and photocurrent. Therefore, the detectivity for the thick barrier SLIP is at the same order for the thin one.

Contents

Chapter 1 Introduction………………………………………………………………1
Reference………………………………………………………………………………3
Chapter 2 Background Introduction………………………………………………..4
2.1 Blackbody radiation……………………………………………………………….4
2.2 Superlattice Structure……………………………………………………………...5
2.2.1 Multiple Quantum Well
2.2.2 Intersubband transition
2.2.3 Group velocity
2.2.4 Relaxation and scattering
2.3 Current Characteristic in the QWIP……………………………………………...10
2.3.1 Photocurrent
2.3.2 Dark Current
2.4 Effect of Doping in the Quantum Well……………………………...……………11
Reference……………………………………………………………………………..13
Chapter 3 Fabrication Process and Measurement of Devices……………………14
3.1 Fabrication Process of the Photodetector………………………………………...14
3.1.1 Sample Cleaning
3.1.2 Lithography
3.1.3 Wet Etching
3.1.4 Electrode Deposition and Liftoff
3.1.5 Anneal
3.1.6 Polishing Facet and Bonding Wire
3.2 Instrument Setup and Measurement……………………………………………...19
3.2.1 Current-Voltage measurement
3.2.2 Spectral Response
3.2.3 Responsivity
3.2.4 Noise Equivalent Power (NEP) and Detectivity (D*)
Reference…………………………………………………………………………….25
Chapter 4 Experiment Result and Discussion…………………………………….26
4.1 Sample structure and operational mechanisms…………………………………..26
4.1.1 Sample structure of S1 and S2
4.1.2 Operational mechanisms
4.2 The experimental data of sample S1…………………………………………......30
4.2.1 Current-Voltage Characteristic
4.2.2 Spectral Response
4.2.3 Specific Detectivity
4.2.4 Summary
4.3 The experimental data of sample S2………………………………...……….…..37
4.3.1 Current-Voltage Characteristic
4.3.2 Spectral Response
4.3.3 Specific Detectivity
4.3.4 Summary
4.4 The Comparisons between S1 and S2…………………………………………....45
4.4.1 The effect of the period numbers
4.4.2 The Effect of the blocking barrier
4.4.3 The Effect of the doped method
4.4.4 The Detectivity
Reference……………………………………………………………………………..55
Chapter 5 Conclusion………………………………………………………….……56

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