Enhanced excitonic emission efficiency in porous GaN and GalnN-GaN quantum wells grown along the polar direction

Porous GaN and (Ga,In)N/GaN single quantum well layers are fabricated using a selective area sublimation (SAS) technique from initially smooth and compact 2-dimensional (D) layers grown on Si(111) or c-plane sapphire substrates
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. Designs of the samples are sketched in figure 1. The optical properties of porous GaN films of different porosities, are investigated focusing on the behaviors of the excitonic features in time-integrated and time-resolved photoluminescence. A substantial enhancement of both excitonic emission intensity and recombination rate, along with insignificant intensity weakening under temperature rise, was observed in the porous GaN films. These observations are in line with i) the local concentration of electric field inside GaN nanoparticles and near pores due to the depolarization effect, ii) the efficient light extraction from the nanoparticles operating as a photonic antenna. Besides this, the porosification enlarges air/semiconductor interface surface that further promotes the extraction efficiency and suppresses non-radiative recombination channels
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as plotted in figure 2. Regarding GalnN-GaN quantum wells, the compressive stress state of the InGaN active layer decreases, then the resulting electric field in the (Ga,In)N quantum well also decreases. Therefore the quantum confined Stark effect is less pronounced and a blue-shift of the QW PL peak is observed. The PL full width at half maximum of the (Ga,In)N QW also decreases in line with this reduction of electric field in the (Ga,In)N quantum well. This is also recorded when measuring the decay times and their evolutions against T as reported in figure 3 and reference 3. This will be discussed extensively.