Room-temperature, mid-infrared (λ=4.7μm) electroluminescence from single-stage intersubband GaAs-based edge emitters

Abstract

GaAs-based, single-stage, intersubband devices with active regions composed of deep quantum wells (i.e., In 0.3 Ga 0.7 As) and high AlGaAs barriers display strong room-temperature emission at = 4.7 m. The structures are grown by metalorganic chemical vapor deposition. The large energy barriers ͑ϳ360 meV͒ for electrons in the upper energy level of the active region strongly suppress both the carrier leakage as well as the tunneling escape rate out of the wells. As a result, the ratio of emissions at 80 and 300 K is as low as 2.0, and thus there is considerably less need for a Bragg mirror/transmitter-type region. Devices with virtually 100% tunneling injection efficiency have been realized, and their room-temperature spectra are narrow: 25 meV full width at half maximum. In the quest to achieve efficient, room-temperature (RT), continuous-wave (cw) laser operation in the mid-infrared (IR) wavelength range (i.e., 3 -5 m) one proposed approach is the use of two-dimensional arrays of unipolar quantum boxes 1 (QBs), with each QB incorporating a singlestage, intersubband-transition structure. In previous work on single-stage, unipolar devices RT intersubband emission has been reported only from InP-based structures 2 at a wavelength of 7.7 m. For 30-to 40-stage GaAs-AlGaAs quantum-cascade (QC) lasers at RT, intersubband emission wavelengths shorter than 8 m cannot be achieved, since at higher transition energies the active-region upper level is apparently depopulated via resonant tunneling between the X valleys of the surrounding AlGaAs barriers. 3 We present here the realization of RT mid-IR electroluminescence emission from single-stage intersubband devices. The RT output power is of the same order of magnitude as that of InP-based QC structures of approximately the same wavelength. The RT emission linewidth is narrow [ϳ25 meV full width at half maximum (FWHM)] and the 80" 300 K emission ratio is very low ͑ϳ2͒.Optimization studies of GaAs-based devices 4 have shown that for thin barriers between the injector region and the active region, two effects occur which cause significant decreases in the upper-(energy) state injection efficiency: (1) a diagonal radiative transition from the injector-region ground state, g, to an active-region lower state, and (2) severe carrier leakage from the state g to the continuum. Here we show that by using GaAs-based devices with very deep active quantum wells (QWs), In 0.3 Ga 0.7 As active layers sandwiched between Al 0.8 Ga 0.2 As barriers, we can virtually suppress carrier leakage to the continuum. Furthermore, since GaAs/ AlGaAs superlattices do not need to be used on both sides of the active region, resonant tunneling cannot occur between X valleys at high transition energies, and thus RT emission in the mid-IR range becomes possible for GaAs-based devices.The material used in the devices is grown by lowpressure metalorganic chemical vapor deposition (MOCVD) at 700°C and is essentially a single-stage structure embedded in a plasmon-enhanced n-GaAs waveguide, 3,4 which gives an op...

InGaAs/GaAsP/AlGaAs, deep-well, quantum-cascade light-emitting structures grown by metalorganic chemical vapor deposition

“…The narrow spectral width of the FTIR absorption spectra as well as the relatively large PVR ratio observed for the In 0.3 Ga 0.7 As/AlGaAs RTDs is good indications that both the single and double QW structures do not exhibit significant strain relaxation and have good interfacial characteristics. Furthermore, previous studies [7] PVRs ≈ 1.5 [12] from conventional 5 mm emitting QC structures grown by MBE.…”

“…The energy separation (dE ¼ 300 meV) between the upper lasing state, E 3 , and the conduction-band edge of the exit barrier is about twice higher than that of conventional InGaAs/ AlInAs/InP QC structures [1][2][3][4]19]. This, in turn, suppresses thermionic carrier leakage at RT to the continuum, as shown on single-stage, deep-well structures [7]. The Bragg reflector structure (i.e., InGaAs/GaAsP) is different from the injector structure, due to the deep-well activeregion design, and can thus be optimized independently of the injector region structure [5].…”

“…Furthermore, unlike conventional QCLs, high-power, high-wallplug-efficiency operation would be maintained at temperatures well above RT. In initial efforts, we have grown and fabricated InGaAs/ AlGaAs/GaAs-based, deep-well light-emitting structures, which provided the first RT emission in the midinfrared (IR) (l ¼ 4.7 mm) from single-stage intersubband devices [7].…”

Progress towards intersubband quantum-box lasers for highly efficient continuous wave operation in the mid-infrared

“…The proposed QBs do not involve self-assembly, but actual fabrication [23], thus allowing to tightly confine the carriers to the QBs. Due to the deep-QW proposed design carrier leakage will be suppressed as already experimentally demonstrated for single-stage QW devices [24]. Thus truly deep QBs could be realized for the first time, which in turn will allow for temperature-insensitive characteristics and subsequent high wallplug efficiencies and long-term device reliability.…”

High-power continuous-wave mid-infrared quantum cascade lasers based on strain-balanced heterostructures (Invited Paper)

“…GaAs/AlGaAs QCLs suffer from X-valley leakage at short wavelengths and as a result, the shortest laser wavelength demonstrated in this material system is around 8 microns 6 at room temperature with reports of emission as short as 4.7 µm without a feasible laser structure having been realized. 7 In contrast to the GaAs/AlGaAs system, the In x Ga 1-x As/Al y In 1-y As system is capable of very deep quantum wells without serious interaction from Xand L-valley electrons. This has been reported by various groups through use of strain balancing.…”