Process Research Of Ohmic Contact On GaAs Based High Power Laser Diode

With the rapid development of GaAs high power lasers,the performance of devices needs to be continuously improved.However,series resistance greatly hinders the performance improvement of devices.The series resistance introduced by the ohmic contact not only affects the operating voltage of device,but also affects the conversion efficiency,output power and the thermal stability of device,which directly affects reliability and lifetime of device.This paper focuses on the ohmic contact of GaAs based semiconductor lasers.Including the optimization of annealing process,the mechanism analysis of thermal diffusion,and the optimization of series resistance of GaAs based semiconductor lasers.The main conclusions are as follows.The effect of annealing parameters on the ohmic contact of n-GaAs and p-GaAs was investigated.The I-V characteristics of n-GaAs and p-GaAs samples at different annealing temperatures indicate that when the alloy temperature is higher than 380℃,the n-GaAs sample transitions from a typical Schottky contact to an ohmic contact,while the p-GaAs sample still shows a typical ohmic contact after annealing.The specific contact resistivity test results based on the dot transmission line model(CTLM)show that the specific contact resistivity of the ohmic contact formed by the n-GaAs and the Ni/Ge/Ni/Au/Ti/Au multilayer metal reaches a minimum value of 3.8×10-5Ω·cm2 until the annealing parameter is 420℃ for 80s,and the minimum specific contact resistivity of the non-alloy ohmic contact formed by the p-GaAs and the Ti/Pt/Au multilayer metal is 5.2×10-6Ω·cm2.The results of surface morphology analysis show that the metal surface shrinkage occurs on the surface of the n-GaAs sample after annealing,while the surface morphology of the p-GaAs sample before and after annealing is smooth.The thermal diffusion mechanism of n-GaAs and p-GaAs forming an ohmic contact was analyzed.Energy dispersive X-ray spectroscopy(EDX)tests show that during n-GaAs alloying,GaAs decomposes Ga to diffuse outward leaving Ga vacancies in GaAs and Ge elements diffused into GaAs occupy Ga vacancies to form donor impurities.As the temperature increases to 380℃,the more Ga vacancies are generated,the higher the donor concentration of Ge is formed by Ga,and a highly doped n+region can be formed on the n-GaAs surface,which formed a good ohmic contact through tunneling.The EDX spectrum of p-GaAs samples shows that the degree of interdiffusion between elements of p-GaAs and Ti/Pt/Au multilayers is small after annealing.It is because the tunneling effect of the highly doped p-GaAs surface causes the formation of an ohmic contact of a non-alloy type.The effects of different electrode structures and annealing parameters on the series resistance of semiconductor lasers were investigated.Four electrode structures were prepared and alloyed at 380℃ for 60 s and 420℃ for 80 s,respectively.The results show that the series resistance is reduced by 14%～20%,the output power is increased by 2%～2.2%,and the conversion efficiency is increased by 1.69%～2.16%of the laser prepared by ohmic contact optimized alloy parameters at 420℃ for 80s.