Realizing Bose-Einstein condensation (BEC) has found intense interest. Up to now extreme conditions like very low temperature and high magnetic field were usually necessary to achieve BEC for low density systems consisting of atoms. Recently, many efforts have been devoted to finding a solid-state system in which BEC can take place. Photoexcited excitons as light-mass bose particles, consisting of bound electron–hole pairs in semiconductors, had triggered intense interest for long time. Excitons as bosons, which can be generated at high density in semiconductor quantum wells, are potential candidates to realize exciton condensation. If their binding energy is higher than kT, which is given for excitons in gallium nitride (GaN) with binding energy of 48 meV, additional confinement in a quantum well (QW) should increase the interaction between excitons and thus offer the chance to observe exciton condensation.

To bring BEC into daily applications, it is highly desirable to realize BEC in a real-world device at room temperature (RT) and free from extreme conditions. Here, we report a simple way to realize boson condensation in a low energy state in GaN-based multi-quantum-well (MQW) laser diodes (LD) at RT. It is revealed by the analysis of abnormal electrical and optical behaviour of GaN-LDs. At threshold, due to the piezo-phototronics effects and the coherent light field, the involved excitons (bosons) in the QW, as dipoles, behave collectively with identical energy and the same direction, which means that they condense into a coherent low energy state. This is confirmed by a redshift of electroluminescence spectra. This quantum effect corresponds to a phase transition in a far-from-equilibrium system, which is an open system exchanging matter and energy with the outside.