Electric Field and its Effect on Hot Carriers in InGaAs Valley Photovoltaic Devices

To maintain a hot carrier population in a robust manner under standard operating conditions, a valley photovoltaics device employs the mechanisms of photoexcited and field aided intervalley scattering to transfer carriers to upper metastable valleys of the band structure. Prior work has demonstrated transfer and storage of enhanced carrier temperatures, a robust effect even at low illumination in comparison to the phonon bottleneck method of hot carrier maintenance. In order to deconvolve the photoexcited intervalley scattering and electric field-aided transfer mechanisms, the previous 20 nm n+-In0.52Al0.48As /250 nm n-In0.53Ga0.47As /1000 nm p+-In0.52Al0.48As /p-InP substrate proof-of-concept device structure was altered to create a set of 25 nm and 100 nm absorber thickness devices, grown by molecular beam epitaxy, then enhanced by a 150 nm ITO top reflective coating. The alteration of the absorber thickness was modeled in NRL Multibands® and shows that as they become thinner, the samples substantially enhance the electric field produced around the interfaces as a result of the doping density. This allows for a series of illumination power dependent photoluminescence measurements with high power 532 nm and 1064 nm laser light, to excite carriers both above and below the upper L valley. This was performed at a range of applied bias voltages to further modulate the electric field strength and investigate its impact, guided by accompanying current density-voltage measurements. From the natural logarithm of the high energy tail of the photoluminescence spectrum, a temperature indicative of the carrier distribution can be determined, revealing both the enhanced carrier temperature even at low illumination seen in prior valley photovoltaic devices and, additionally, a phonon bottleneck-type increase in temperature with increasing power.