The typical device performance is shown in the accompanying figure. The signal is measured from a single micro-column with mesa dimensions of 15 µ by 15 µ, within a patterned array of 100 micro-columns. Voltage applied to the device was scanned from 0 to -4 volts. Observed optical power in μW (black) is shown at left, while device resistance (red) is shown at right. Optical curves show exponential dependence of output power on applied voltage (Note, the optical signal has an onset threshold at approximately -1V.).
The increase in device resistance with voltage is attributed to opening one more channel of relaxation for minority electrons by generating non-equilibrium magnons. Optical detection was made using a Genetec radiometer and recorded the total emission from 1 to 30 terahertz. The total power output from a single multilayer column at -4V was about 23 μW. Thus, for an array of 100 micro-columns, the total output obtained would be 2.3 mW. In our setup, the radiometer picks up only ~30% of the generated energy.