Optically Pumped Nonpolar GaN/AlGaN Quantum Well Intersubband Terahertz Laser Active Region Design

The terahertz frequency (THz) range (wavelengths from30μm to1000μm) remains one of the least developed spectral regions. Although the firstTHz QCL operated up to a maximum temperature of T=50K andimprovements in active regions and waveguides have brought substantialprogress in GaAs/AlGaAs based QCL working temperature (Tmax=199.5K),room-temperature operation of THz lasers will require an additionalrevolution either through the invention of an alternative active region design,or through the use of a new system. Thermal backfilling is one of the majorprocesses causing a degradation of population inversion in THz QCL at hightemperatures. In GaAs-based material system, in order to take advantage ofthe resonant LO phonon effect, the energy separation between the lower laserstate and the ground state where the majority of the electrons reside is justabove the LO phonon energy (~36meV), which is comparable to roomtemperature kBT (~26meV). In addition, QCLs based on semiconductors suchas GaAs/AlGaAs are not capable of emitting in the energy range around theLO phonon energies (ELO~36meV in GaAs), leaving a gap in the spectralrange between30and40μm.In contrast to QCL, which is electrically pumped, optically pumped intersubband lasing offers the advantage of highly selective excitation ofcarriers into the desired subband and thus provides a tool for the study oflasing mechanism, carrier relaxation, and other processes.We propose an optically pumped nonpolar GaN/AlGaN quantum well(QW) active region design for terahertz (THz) lasing in wavelength range of(LO) phonon scattering in GaN/AlGaN QWs is used to depopulate the lowerlaser state, and more importantly the large LO phonon energy is utilized toreduce the thermal population of the lasing states at high temperatures. Theinfluences of temperature and pump intensity on gain and electron densitieswere investigated. Based on our simulations, we predict that with sufficientpump intensity, a room temperature operated THz laser using nonpolarGaN/AlGaN structure is realizable.This work is supported by the National Major Basic Research Project(2011CB925603) and the Shanghai Municipal Major Basic Research Project(09DJ1400102).