Electrical Measurement of Recombination Lifetime in Blue Light Emitting Diodes
- PDF / 172,644 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 201 Views
B2.11.1
Electrical Measurement of Recombination Lifetime in Blue Light Emitting Diodes M.A. Awaah, R. Nana1 and K. Das Department of Electrical Engineering, Tuskegee University, Tuskegee AL 36088 1. Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA.30332 ABSTRACT A recombination lifetime of approximately 25 ns was extracted from measured reverse recovery storage times in AlGaN/GaN/AlGaN double heterojunction blue light emitting diodes. This experimentally determined lifetime is expected to arise from a combination of radiative and non-radiative processes occurring in the diodes. The non-radiative processes are likely to be due the presence of a high concentration deep-states as identified from the current-voltage and capacitance-voltage measurements. Current-voltage characteristics of these diodes were highly non-ideal as indicated by high values of the ideality factor ranging from 3.0 – 7.0. Logarithmic plots of the forward characteristics indicated a space-charge-limited-current (SCLC) conduction in presence of a high density of “deep-level states” in the active region of the diodes. An analysis of these characteristics yielded an approximate density of these deep-level states as 2 x 1017/cm3. The density of deep-states extracted from capacitance-voltage measurements were in good agreement with that obtained from current-voltage measurements. INTRODUCTION Gallium nitride and its related alloys are particularly attractive for optoelectronic and electronic applications due to their direct wide bandgap (3.4 eV) [1,2], high thermal conductivity and radiation hardness. Though the band-edge emission in GaN occurs at about 362 nm, in the ultraviolet region of the electromagnetic spectrum, by appropriately alloying GaN with AlN and InN, the energy band gap of the resulting AlInGaN can be altered for emission in the ultraviolet to yellow or even red region by varying the composition of Ga, Al and In. With the recent demonstration of high-intensity blue light emitting diodes (LEDs) and laser diodes, it becomes important to gain a better understanding of the radiative and nonradiative processes occurring in the material system. Herteroepitaxial growth, of GaN films used in the fabrication of LEDs, contributes to high density of crystallographic defects [3,4]. These defects are likely to contribute to competing nonradiative transitions of injected carriers, thus reducing the efficiency of optical emission. Various research groups have studied the radiative and non-radiative recombination processes in GaN based LEDs using mostly optical techniques [5-10]. These studies focused on AlGaN/InGaN/AlGaN double heterojunction based LED structures grown primarily on sapphire substrate. The work reported here involves a study of AlGaN/GaN/AlGaN DH LEDs, grown on SiC substrates, using electrical measurements for the determination of recombination lifetime of injected carriers and an approximate concentration of defects considered to be responsible for nonradiative processes occurring in these diodes. EX
Data Loading...
