Electron beam pumping in nitride vertical cavities with GaN/Al 0.38 Ga 0.62 N Bragg reflectors

Abstract

Electron beam pumped surface emitting lasers are of great interest for a variety of applications, such as Laser Cathode Ray Tubes (LCRT) in projection display technology and high power UV light sources for photolithography as an application of nitride emitters. Two distributed Bragg reflector (DBR) samples were grown by plasma assisted molecular beam epitaxy (PAMBE). The active regions of the samples are a GaN bulk layer and multihetero (MH) structure, respectively. Also, a separately grown single DBR stack was studied to find optical transmission and reflection properties which were compared to transfer matrix simulations. Scanning electron beam pumping at 80 K was performed on the two vertical cavity structures with an excitation energy of 40 keV in order to characterize the influence of the distributed Bragg reflectors on the resonator properties. Surface emission spectra measured for various electron beam currents revealed luminescence emission maxima located at about 3.45 eV at 80 K for the sample with the MH structure active region. Optical modes appeared for excitation powers greater than 0.85 MW/cm<SUP>2</SUP>. Further increasing the excitation power density the number of modes increased and a broadening and redshift of the luminescence spectrum could be observed. Based on our experimental results, we discuss the dependence of optical parameters of the nitride vertical cavity and sample surface reactions on primary electron beam power.