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The polarization discontinuity across interfaces in polar nitride-basedheterostructures can lead to the formation of two-dimensional electron and holegases. In the past, the observation of these electron and hole gases has beenachieved through various experimental techniques, most often by electronicmeasurements but occasionally by optical means. However, the occurrence of atwo-dimensional hole gas has never been demonstrated optically. The objectiveof this article is to demonstrate, thanks to the combination of various opticalspectroscopy techniques coupled to numerical simulations, the presence of atwo-dimensional hole gas in a GaN/AlGaN/GaN heterostructure. This is madepossible thanks to a GaN/AlGaN/GaN heterostructure displaying amicrometer-thick AlGaN layer and a GaN cap thicker than in conventionalGaN-based HEMTs structures. The band structure across the whole heterostructurewas established by solving self-consistently the Schr\"odinger and Poissonequations and by taking into account the experimentally determined strain stateof each layer. Continuous and quasi-continuos photoluminescence reveal thepresence of a broad emission band at an energy around 50 meV below the excitonemission and whose energy blueshifts with increasing excitation power density,until it is completely quenched due to the complete screening of the internalelectric field. Time-resolved measurements show that the emission arising fromthe two-dimensional hole gas can be assigned to the recombination of holes inthe potential well with electrons located in the top GaN as well as electronfrom the bottom AlGaN, each of them displaying different decay times due tounequal electric fields. Besides the optical demonstration of a two-dimensionalhole gas in a nitride-based heterostructure, our work highlights the opticalrecombination processes involved in the emission from such a hole gas.

Experimental demonstration of a Two-Dimensional Hole Gas (2DHG) in a GaN/AlGaN/GaN based heterostructure by optical spectroscopy