PhD Dissertation Defense by Ahmad Mansoori on Reducing threading dislocations in GaSb epilayer grown on GaAs substrate for photovoltaic and thermophotovoltaic applications

Departmental News

Ahmad Mansoori

Posted: March 20, 2019

Date: Monday, March 25, 2019 

Time:  1:00 PM to 2:30 PM

Location:  CHTM, Room 101

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Mr. Ahmad Mansoori

OSE Ph.D. Candidate

Committee members:

Dr. Ganesh Balakrishnan, Committee Chair

Dr. Francesca Cavallo

Dr. Payman Zarkesh-Ha

Dr. Adam Hecht


GaSb based photovoltaic devices have been demonstrated on GaAs substrates by an inducing interfacial array of 90° misfit dislocations. Despite the beneficial qualities of the highly stable 90° misfit dislocation, there is a significant density of residual threading dislocations in the GaSb layer, resulting in the degradation of the electrical performance of such photovoltaic cells compared to lattice matched devices. We aim to reduce threading dislocation density by optimizing growth temperature and by using an AlSb dislocation filtering layer. The growth temperature optimization results in a reduction of the threading dislocation density to 1.3 × 108 cm −2 . Adding an AlSb dislocation filtering layer further improves the electrical performance of the GaSb solar cells by reducing the threading dislocation density to 4 × 107 cm−2 . A comparison between the experimental data and theoretical calculation confirms that the recombination in dislocation centers is a dominant loss mechanism in GaSb solar cell grown on GaAs substrate. Also, the band offset between AlSb/GaSb is not proper for photovoltaic application and block the photogenerated carrier to reach a contact. InGaSb strained layer was chosen as replacement of AlSb defect filtering layer. Effect of strain, thickness, and a number of InGaSb defect filtering layer on the electrical performance of GaSb photovoltaic cell grown on GaAs was tested. Strain, thickness and number of defect filtering layer optimization results in improvement of normalized open circuit voltage from 43% to 77% and short circuit current from 59% to 78% in GaSb photovoltaic cell.