Simpson Chua Ying Chao

        

 

Contact Information:

Simpson Chua
Bell Engineering Center
Fayetteville, AR. 72701
Email: ychua@uark.edu

 

 

 

 

Education:

• B.S. Electrical Engineering – Telecommunications, University of Louisiana at Lafayette (ULL) (May 2003)

• M.S. Microelectronics-Photonics - University of Arkansas at Fayetteville – (May 2005)

 

Experience:

Spring 2000 – Fall 2002: Computer Lab Supervisor, ULL, Lafayette, LA.

Fall 2002 – Spring 2003: Peer Counseling Tutor, ULL Special Services, Lafayette, LA.

Summer 2003 – Present: Research Assistant, University of Arkansas, Fayetteville , AR.

 

Current Research:

We investigate the optical absorption spectra of intersubband transitions in In_0.3Ga_0.7As/GaAs multiple quantum dots grown by molecular beam epitaxy. By varying the number of In_0.3Ga_0.7As monolayers deposited, a series of samples with varying dot sizes ranging from 10 – 50 monolayers were grown. The optical absorption of intersubband transitions from these samples were studied as a function of the quantum dot size. The measurements were obtained using a Bomem DA8 Fourier Transform Infrared Spectrometer (FTIR). Characterization of the optical absorption was conducted at the normal incidence, Brwester's Angle and waveguide configurations. The samples having waveguide geometry (2.5mm x 7mm x 0.6mm) were fabricated with the beveled facet being polished at 45°. Our results suggested that the quantum dots grown with size less than 15 monolayers or more than 50 monolayers did not yield any observable measurements of intersubband transition. This suggests that there exist a critical upper and lower limit of In_0.3Ga_0.7As quantum dots for infrared detectors. A wavelength range of 8.60 – 13.70 mm is achieved for structures grown with a range of 15 – 50 monolayers of In_0.3Ga_0.7As. The theoretical optical absorption line-shape of the intersubband transition was compared to the experimental measurements. We observed that the intersubband transitions of these samples take the form of a Lorentzian. It is noted however that the line-shape of the sample with 15 monolayers of In_0.3Ga_0.7As is asymmetrical which implies that the intersubband transition is bound to continuum.

In a more recent study, we investigate photoconductivity in Dot-in-a-Well (DWELL) structures from In_0.15Ga_0.85As/InAs. Preliminary results show great potential in utilizing this structure for multi-colored detectors.

Goals:

• To obtain photoconductivity measurements from the series of samples above

• To tune and/or change design parameters to improve optical and electrical characteristics

• To fabricate infrared detectors operating in the far IR.