We investigate the electrical spin injection into (110) GaAs single quantum wells (SQWs) and multiple quantum wells (MQWs) using light-emitting diodes (LEDs) having Fe/crystalline-AlOx (x-AlOx) tunnel barrier contacts. A degree of circular polarization (Pc) of 5.0% is obtained for the SQW LED at 4 K with the current density of 1 kA/cm2 which is comparable to that for the laser oscillation in vertical-cavity surface-emitting lasers (VCSELs). On the basis of electron spin relaxation time and carrier lifetime in the (110) GaAs SQW measured by time-dependent photoluminescence and the value of Pc = 5.0%, the degree of spin polarization of initially injected electrons (P0) in the SQW is estimated to be 6.6% at 4 K. By using the MQW LED having a much stronger electroluminescence, a Pc value of 2.6% is obtained at room temperature (RT) with the current density of 1.5 kA/cm2. The temperature and current density dependences of Pc are found to be weak in both the SQW and MQW LEDs. The estimated P0 of 9.3% at RT suggests that the Fe/x-AlOx contacts can be used for the RT electrical spin injection for spin-controlled VCSELs.
ASJC Scopus subject areas
- Physics and Astronomy(all)