Junction Temperature Measurements in InGaAs 1064 nm Laser Power Converters

Laser power beaming (LPB) allows for wireless power transmission on demand, enabling future missions for extraterrestrial exploration and colonization, as well as continuous flight of unmanned aerial vehicles and emergency power in natural disaster zones on Earth. To surpass the valley of death, these systems will have to prove their reliability in a variety of operating conditions and under high laser power intensity. The two largest barriers to commercial buy-in identified in our research were full-scale demonstrations of reliability and thermal handling. In this work, we address thermal handling. Here, we present junction temperature measurements for our In0.20Ga0.80As laser power converters accomplished by the transient or fast-Voc method. Unlike other methods which can only measure the surface temperature of a device, this method capitalizes on the exponential change of open circuit voltage (VOC) with temperature to get internal junction temperature. The device is held at a steady temperature with an active cooling stage, then suddenly illuminated by a 1070 nm laser by opening a fast optical shutter. The VOC is then measured over the course of several seconds, revealing a peak voltage (VP) and a steady state voltage (VSS) which can be used to calculate the junction temperature. Our devices showed that at low laser irradiances, the device stabilized near the active cooling stage temperature, but at high irradiances the devices could stabilize up to 37oC higher than the stage temperature. To the knowledge of these authors these devices were measured over a larger temperature range down to cryogenic temperatures and utilize a different laser/LPC wavelength than previous studies.