Do III-V based photovoltaics "glow" (photo-luminesce) when illuminated but not loaded?

Question

In this nice answer I started to learn about how the silicon photovoltaics cells on the International Space Station are managed. In that case, the cells are generally either delivering useful power to the station, or shunted to a dummy load. However, some satellites may leave some fraction of their photovoltaics open circuit if there is low power demand. In that case, the electron-hole pairs produced by sunlight are left to recombine within the junction itself.

Does this mean that photovoltaic cells made from III-V compounds with direct band gaps would produce measurable amounts of photoluminesence under solar illumination, at a wavelength roughly corresponding to the local band gap - there might be heterostructures so the wavelength may not correspond to bulk material band gap.

InP (in the past), InGaAs and GaAs based semiconductor junctions are often used. Many high power telecommunications satellites in geostationary orbits use multi-junction cells that are made from GaAs based semiconductor materials. If I pointed a (near IR capable) telescope at one (for example using this clever technique), and used a filter, could I detect this luminescence?

A lot of exotic processes in devices that include semiconductor junctions can make tiny amounts of light - I'm interested in the main, strong radiative recombination in direct band gap materials with quantum efficiencies of say 1% or greater. Thus the "glow" in the title.

Answer 1

III-V photovoltaics will indeed photoluminesce quite nicely (particularly if not loaded). As you note, they are direct band gap materials so if there is any overlap of electrons and holes you can get recombination with the accompanying photons.

If connected to an external circuit, the electron/hole pairs generated will get swept out of the junction fairly quickly, reducing the possibility of recombination. You will still have recombination in the 'bulk' contact areas where the e-h pairs are 'wasted'. In addition, depending on the junction design, you can actually get quite a bit of minority carrier diffusion (not drift) out of the junction in to less hospitable areas.

If not connected to a circuit, you will end up having all the e-h pairs recombine within the material (they aren't going anywhere else), so it is just like doing photoluminescence on bulk material.

Photoluminescence of silicon solar cells, particularly at the wafer level, has been done regularly for the development of high-efficiency material (for, e.g., space applications where that last 0.5% counts). Since silicon is an indirect gap material with nominally long carrier lifetimes, the intensity of the phonon-assisted optical transition is a good indicator of the (non-radiative) defect levels in the material.

As for III-V devices, they all luminesce quite nicely in normal operation. A forward-biased junction results in electrons and holes flowing in from opposite directions to annihilate each other, releasing lots of photons. My lab does radiation effects on devices, and the die have to be bare (unlidded) to hit them with an ion beam. The targeting camera shows the devices lit up brightly. The first time I saw it I could not help a 'Cool - look at that!' coming out of my mouth, at which time the staff member running the experiment commented in an even voice 'GaAs is a direct gap material, Jon'. It is one of those things that you kind of don't directly connect in device physics courses...