An Investigation into the Effects of n-type Doping in InAs Quantum Dot Infrared Photodetectors Steven P. Minor Group: Brandon Passmore, Jiang Wu, Dr. Manasreh, Vasyl Kunets, & Dr. Salamo Microelectronic-Photonics REU University of Arkansas July 25, 2007

Presentation Outline  Introduction to Quantum Dots Infrared Photodetectors (QDIPs), Interband and Intersubband Transitions  Experimental Design  Results  Conclusion  Acknowledgements

Why are QDIPs important?  Two significant advantages over the one dimensionally confined Quantum Well Infrared Photodetector (QWIP) Can operate at normal incident light due to the three dimensional carrier confinement. Can operate at near room temperature due to high photoconductive gain and low noise.

What’s a Quantum Dot?  Also known as artificial atoms.  Carriers are confined in three-dimensions.  An example would be InAs grown on GaAs.

Interband Transition  Interband transitions occur when electrons in semiconductor materials absorb photons and are excited from the valence band to the conduction band.

Intersubband Transitions  Intersubband transitions are optical excitations between the quantized energy levels within the conduction band of semiconductor heterostructures.

Different types of Quantum Emission  Thermionic Emission is the flow of charged particles called thermions from a charged metal or a charged metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface.  Field-assisted tunneling occurs when electrons pass through a barrier in the presence of a high electric field.

Molecular Beam Epitaxy (MBE)

Growth Objectives  Vary carrier concentrations in the Quantum Dots Control Sample: Undoped Dependent Samples:  1 x cm -3  5 x cm -3  1 x cm -3 S.I. GaAs (100) Substrate 50 nm GaAs Spacer 2 ML InAs QDs 50 nm GaAs Spacer x nm n-GaAs: Si 2 x cm nm n-GaAs: Si 2 x cm -3

Spin Coater (CEE-100)

Mask Aligner (K.S.- MJB3)

Electron Beam Evaporator (Edwards 306)

Fabricated Devices

Measurement Equipment  Doping Concentrations Accent Electrochemical Capacitance-Voltage Pro  Photoluminescence Bomem Fourier-transform Infrared Spectrometer  Current-Voltage Keithley Semiconductor Characterization system  Photoresponse Bruker Fourier-transform Infrared Spectrometer Standford Research System low-noise preamplifier

Results  ECV

Results  Photoluminescence

Results  Dark Current  Measured at 77 K

Results  Photoresponse  Measured at 77 K. Carrier concentration (cm -3 ) Bias Voltage (V) undoped1.1 1E E E

Results  Atomic Force Microscope (AFM)

Results  Used a computer program to detect dots and calculate the average quantum dot density per cm 2.  Averages Dot Height: 5 nm Lateral Diameter: 28 nm Dot Density: 2.44 x cm -2

Results 3D Carrier Concentration (cm -3 ) 2D Carrier Concentration (cm -2 ) 2D Dot Density (cm -2 ) Electrons/Dot 5.00E E E E E E E E E+1120  Optimal Photoresponse was observed from the sample in which the carrier concentration donated 2 electrons per dot.

Conclusion  Introduced to graduate level research  Learned about nanostructures and infrared photodetectors  Experimentally verified previous research results

Acknowledgements Dr. Manasreh Brandon Passmore Jiang Wu Vasyl Kunets Eric Decuir Dr. Salamo Ken Vickers and Renee Hearon

References  B. F. Levine, “Quantum well infrared photodetectors,” J. Appl. Phys.,vol. 74, p. R1,  M. O. Manasreh, Semiconductor Heterojunctions and Nanostructures. New York: McGraw-Hill, 2005, ch. 10, pp. 457–528.  Shih-Yen LIN, Yao-Jen TSAI and Si-Chen LEE, “Effect of Silicon Dopant on the Performance of InAs/GaAs Quantum-Dot Infrared Photodetectors,” Japanese J. Appl. Phys., Vol. 43, No. 2A, 2004, pp. L 167–L 169  J. Phillips, K. Kamath, X. Zhou, N. Chervela, and P. Bhattacharya, “Photoluminescence and far-infrared absorption in Si-doped self-organized InAs quantum dots,” Appl. Phys. Lett. 71 (15), 13 October  A. D. Stiff-Roberts, X. H. Su, S. Chakrabarti, and P. Bhattacharya,” Contribution of Field-Assisted Tunneling Emission to Dark Current in InAs–GaAs Quantum Dot Infrared Photodetectors,” IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 16, NO. 3, MARCH  Jie Liang, Ying Chao Chua, M. O. Manasreh, Euclydes Marega, Jr., and G. J. Salamo, “Broad-Band Photoresponse From InAs Quantum Dots Embedded Into InGaAs Graded Well,” IEEE ELECTRON DEVICE LETTERS, VOL. 26, NO. 9, SEPTEMBER 2005.