臺灣博碩士論文加值系統

本論文詳細研究了第二類碲化鋅/硒化鎘多重量子井之光電特性，文中許多有趣的結果有助於增進對此材料之了解與應用。
I. 室溫下碲化鋅/硒化鎘多重量子井之準束縛態的存在
我們利用光子調制反射光譜，無接點式電場調制反射光譜及光電導的測量來觀測室溫下準束縛態存在於第二類碲化鋅/硒化鎘多重量子井的位障之上。此束縛態與一般之研究極為不同, 因一般所研究之束縛態是位在量子井內。我們提供了明顯的證據來證明自由載子侷限在位障層上(不是在價電帶硒化鎘層就是在導電帶碲化鋅層)確實存在。我們發現位障層的寬度和位障層上基態躍遷能量之關係可以用建設性干涉條件做很好的描述。我們也利用光電導和光激發螢光光譜量測到介於電子侷限在硒化鎘層和電洞侷限在碲化鋅層之間的吸收性及輻射性間接躍遷。
II. 碲化鋅/硒化鎘多重量子井之持續性光電導的研究
在第二類碲化鋅/硒化鎘多重量子井中，我們觀測並研究了持續性光電導的現象。持續性光電導的衰減動力學可以用一個扭曲的指數方程式 , 做很好的描述。在特定的溫度區域中，我們很驚訝地發現持續性光電導的衰減時間隨著溫度增加而增加。這種特殊的實驗結果和已刊出的文獻相當不同，而且無法用現有的模型去解釋。經由不同條件下持續性光電導的研究，如不同的溫度、不同的激發光能及不同的硒化鎘層寬度，我們指出，由於界面粗糙所造成的界面位能起伏是第二類碲化鋅/硒化鎘多重量子井中持續性光電導效應的來源。

In this thesis we report the studies of optical and electrical properties on type-II ZnTe/CdSe multiple quantum wells. Quite interesting results have been obtained from our studies which should be very useful for the enhancement of our understanding and application in this material.
I. Observation of quasibound states in type-II ZnTe/CdSe superlattices studied by modulation spectroscopies and photoconductivity at room temperature
We report that the quasibound states at the above-barrier region in type-II ZnTe/CdSe superlattices can be clearly observed at room temperature by photoreflectance (PR), contactless electroreflectance (CER) as well as (PC) measurements. We provide concrete evidence to confirm that free-carrier confinement at barrier layer ( either in the valence-band CdSe layer or in the conduction-band ZnTe layer) does exist. It is found that the barrier-width dependence of the above-barrier ground state transition energies can be described well by the constructive interference condition. We also observe the absorptive and radiative spatially indirect transition between electrons confined in the CdSe and holes confined in the ZnTe layers by photoconductivity (PC) and photoluminescence (PL) measurements, respectively.
II. Study of persistent photoconductivity in type-II ZnTe/CdSe superlattices
Persistent photoconductivity (PPC) has been observed and investigated in type-II ZnTe/CdSe superlattices grown by molecular beam epitaxy (MBE) on (100) GaAs substrates.. The decay kinetics of the PPC effect can be well described by a stretched-exponential function, , . Quite surprisingly, we discovered that the PPC decay time increases with increasing temperature in a certain temperature region. This behavior is different from the previous reports and can not be explained by the existing models. Through the studies of the PPC effect under various conditions, such as different temperature, different photon energy of photoexcitation, and different CdSe layer width, we suggest that the interface potential fluctuations induced by inteface roughness are the origin of the PPC effect in type-II ZnTe/CdSe superlattices.

Contents
1.Preface1
2.Theoretical Background6
2.1Modulation Spectroscopy6
2.1.1Experimental System Setup7
2.1.2Modulation Techniques9
2.1.2.1Photoreflectance (PR)10
2.1.2.2Contactless Electroreflectance (CER)11
2.1.3Lineshape Consideration for Modulation Spectroscopy14
2.1.4Methods of Theoretical Calculation (Envelope Function Approximation in Semiconductor Microstructure)16
2.1.4.1Schrödinger Equation and Boundary Conditions16
2.1.4.2Runge-Kutta Method18
2.2Photoluminescence (PL)21
2.3Photoconductivity (PC)21
2.4Persistent Photoconductivity (PPC)23
2.4.1Macroscopic Barrier (MB) model23
2.4.2Large-Lattice-Relaxation (LLR) model25
2.4.3Random-local-potential fluctuation (RLPF) model27
2.5References30
3.Observation of quasibound states in type-II ZnTe/CdSe superlattices studied by modulation spectroscopies and photoconductivity at room temperature34
3.1Introduction34
3.2Sample Preparation36
3.2.1Crystal Growth36
3.2.2Band Structure39
3.3Experiment41
3.4Results and Discussions45
3.5Summary56
3.6References57
4.Study of Persistent Photoconductivity in type-II ZnTe/CdSe superlattices59
4.1Introduction59
4.2Experiment62
4.3Results and Discussions64
4.4Summary75
4.5References76
5.Conclusion78

1.T. Tao, in The Technology and Physics of Molecular Beam Epitaxy, edited by E. H. C. Parker (Plenum, New York, 1985), p. 313.
2.N. Samarth, H. Luo, J. K. Furdyna, S. B. Qadri, Y. R. Lee, R. G. Alonso, E. K. Suh, A. K. Ramdas, and N. Otsuka, Surf. Sci. 228, 226 (1990).
3.N. Samarth, H. Luo, J. K. Furdyna, S. B. Qadri, Y. R. Lee, A. K. Ramdas, and N. Otsuka, Appl. Phys. Lett. 54, 2680 (1989).
4.H. Luo, N. Samarth, F. C. Zhang, A. Pareek, M. Dobrowolska, J. K. Furdyna, K. Mahalingam, N. Otsuka, W. C. Chou, A. Petrou, and S. B. Qadri, Appl. Phys. Lett. 58, 1783 (1991).
5.P. Voisin, G. Bastard, and M. Voos, Phys. Rev. B 29, 935 (1984).
6.W. A. Harrison and J. Tersoff, J. Vac. Sci. Technol. B 4, 1071 (1986).
7.E. T. Yu, M. C. Phillips, J. O. McCaldin, and T. C. McGill, J. Vac. Sci. Technol. B 9, 2233 (1991).
8.H. Luo, W. C. Chou, N. Samarth, A. Petrou, and J. K. Furdyna, Solid State Commun. 85, 691 (1993).
9.F. C. Zhang, H. Luo, N. Dai, N. Samarth, M. Dobrowolska, and J. K. Furdyna, Phys. Rev. B 47, 3806 (1993).
10.L. L. Chang, G. A. Sai-Halasz, L. Esaki, and R. L. Aggarwal, J. Vac. Sci. Technol. 19, 589 (1981).
11.B. A. Wilson, IEEE J. Quantum Electronics 24, 1763 (1988).
12.K. Maschke, P. Thomas and E. O. Gobel, Phys. Rev. Lett. 67, 2646 (1991).
13.G. Bastard, Wave Mechanics Applied to Semiconductor Heterostructures (les editions de physique, Les Ulis, France) (1988).
14.E. T. Yu, Y. Rajakarunanayake, M. C. Phillips, J. O. McCaldin, and T. C. McGill, presented at the 1990 International Conference on Solid State Devices and Materials, Sendai, Japan, 1990.
15.J. O. McCaldin and T. C. McGill, J. Vac. Sci. Technol. B 6, 1360 (1988).
16.J. O. McCaldin, in Growth and Optical Properties of Wide-Gap II-VI Low-dimensional Semiconductors, edited by T. C. McGill, C. M. Sotommayor-Torres, and W. Gebhardt (Plenum, New York, 1988), p. 39.