Improvement of Electrical Characteristics of Silicon Diode by Using Q-Switched Nd YAG and CO2Lasers

Abstract

In this work, enhancement of defects arising from conventional thermal annealing, electrical characteristics and dynamic resistance of silicon diode has been carried out by using two types of lasers in order to improve the electrical characteristics of these silicon diodes First: Q-switched Nd:YAG laser (1064 nm) was applied with pulse energy of 1000 mj with repetition rate of 3,4 and 5 Hz, respectively. The Results obtained from the I-V characteristics of silicon diode showed an improvement in the curve behavior, and the dynamic resistance. Calculations based on diode I-V characteristic, showed a decrease in dynamic resistance value from 3.56 to 2.64 Ω, and the forward voltage from 0.7 to 0.64 V with increasing pulse repetition rate to 5 Hz. The Scanning Electron Microscope (SEM) images showed also a reduction of defects in silicon diode surface after laser annealing. In the case of the silicon diodes which were irradiated by Q-switched Nd:YAG laser (532 nm) with energy dose ranged between 1×〖10〗^(-9) and 1.8×〖10〗^(-9) J, a slight improvement in the surface defects, I-V characteristics, and dynamic resistance were noticed where the dynamic resistance decreased from 3.56 to 3.16 Ω. Second: By using two kinds of CO2 lasers, CW CO2 (λ= 10.6 µm) with power ranged from 5 to 30 W and pulsed CO2 laser with pulse energy ranged between 500 to 600 mJ. In the case of CW laser with irradiation time of 5 seconds for each diode, an improvement in the I-V characteristic curve behavior and decreasing in dynamic resistance was resulted when the laser power reach 15 W, where the dynamic resistance was decreased from 3.16 to 2.6 Ω, and the forward voltage also decreased from 0.7 to 0.597 V. At laser power of 20, 25, and 30 W. The behavior of the I-V characteristics curve was changed, where the forward voltage increased from 0.7 to 0.72 V, and the dynamic resistance also increased from 3.16 to 3.48 Ω when the laser power reached 30 W. The silicon diodes irradiated 5 times for each diode by pulsed CO2 laser with pulse energy ranged from 500 to 600 mJ, the results showed an improvement in the behavior of I-V characteristics curve, where the dynamic resistance and the forward voltage were decreased from 3.16 to 2.56 Ω and from 0.7 to 0.588 V at pulse energy of 600 mJ, respectively. As conclusions, laser irradiation of silicon diodes improves the electrical characteristics of these diodes. The power of the CW lasers and pulse energy beside the frequency are the major parameters affect the diode characteristic. Irradiation by excimer laser for silicon or germanium films, fabrication of gap capacitor and formation of silicide have been suggested as future work.