Recent progress in spin-LED: realization of pure circular polarization EL at room temperature with current density of 10 A/cm2 (Conference Presentation)

Electroluminescence with nearly pure circular polarization (CP) at room temperature (RT) together with electrical helicity control [1, 2] has been demonstrated by a lateral-type spin-polarized light emitting diodes (LT-spin-LEDs) consisting of AlGaAs/GaAs double-heterostructures and the crystalline AlOx (x-AlOx) tunneling barrier [3]. In this LT-spin-LED, relatively high current density of J > 100 A/cm2 was required to achieve the circular polarization of P ~ 0.95. Operation with J > 100 A/cm2, however, often resulted in irreversible breakdown and short-lived spin-LED. In order to suppress this breakdown, we have studied fabrication of LT-spin-LED devices incorporating x-AlOx/AlAs hybrid tunneling barriers. With AlAs layers that are inserted between the x-AlOx layer and a top n-GaAs layer of LT-spin-LED, we aim at reinforcing electrical robustness of x-AlOx layers that are formed by oxidation of Al epilayers at RT. Nearly pure CP emissions (~ 0.92) are obtained from LT-spin-LED devices with hybrid tunneling barriers at J ~ 10 A/cm2. To our surprise, current density for pure CP emission decreases to about one-tenth and the yield of device fabrication is significantly improved (~ 5 % -> ~ 67 %). It is supposed that growth of AlAs layers prior to the formation of x-AlOx layers gives rise to improvement of crystalline quality of x-AlOx layers in terms of suppression of defects in the oxide layer and/or those across x-AlOx/AlAs/n-GaAs interfaces. [1] N. Nishizawa et al., PNAS 114, 1783 (2017). [2] N. Nishizawa et al., APEX 11, 053003 (2018). [3] N. Nishizawa et al., JAP 114, 033507 (2013).