1 Investigation of Electrically Active Defects in InGaAs Quantum Wires Intermediate-Band Solar Cells Using Deep Level Transient Spectroscopy (DLTS) Technique Noor alhuda Al Saqri 1,2,* , Jorlandio F. Felix 3 , Mohsin Aziz 1 , Vasyl P. Kunets 4 , Dler Jameel 1,5 , David Taylor 1 , Mohamed Henini 1 , Mahmmoud S. Abd El-sadek 6 , Colin Furrow 4 , Morgan E. Ware 4 , Mourad Benamara 4 , Mansour Mortazavi 4 , Gregory Salamo 4 1 School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Center, University of Nottingham, Nottingham NG7 2RD, United Kingdom 2 Department of Physics, College of Science, Box 36, Sultan Qaboos University, Al Khoud 123, OMAN 3 Universidade de Brasília, Instituto de Física, Núcleo de Física Aplicada, Brasília, DF, 70910-900, Brazil 4 Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA 5 Department of Physics, Faculty of Science, University of Zakho, Kurdistan Region-Iraq 6 Nanomaterial Laboratory, Physics Department, Faculty of Science, South Valley University, Qena 83523, Egypt Abstract InGaAs Quantum Wires (QWr) Intermediate-Band Solar Cells based nanostructures grown by molecular beam epitaxy (MBE) are studied. The electrical and interface properties of these solar cell devices as determined by current–voltage (I–V) and capacitance – voltage (C-V) techniques were found to change with temperature over a wide range of 20–340 K. The electron and hole traps present in these devices have been investigated using deep level transient spectroscopy (DLTS). The DLTS results showed that the traps detected in the QWr doped devices are directly or indirectly related to the insertion of the Si δ-layer used to dope the wires. In addition, in the QWr doped devices, the decrease of the solar conversion efficiencies at low temperatures and the associated decrease of the integrated external quantum efficiency EQE through InGaAs could be attributed to detected traps E1QWR_D, E2QWR_D and E3QWR_D with activation energies of 0.0037 eV, 0.0053 eV, and 0.041 eV, respectively. Keywords: Quantum Wires Intermediate-Band Solar Cells, I–V, C-V, DLTS, defects