Abstract
A terahertz quantum cascade laser design that combines a wide gain bandwidth, large photon-driven transport and good high-temperature characteristics is presented. It relies on a diagonal transition between a bound state and doublet of states tunnel coupled to the upper state of a phonon extraction stage. The high optical efficiency of this design enables the observation of photon-driven transport over a wide current density range. The relative tolerance of the design to small variations in the barrier thicknesses made it suitable for testing different growth techniques and materials. In particular, we compared the performances of devices grown using molecular-beam epitaxy with those achieved using organometallic chemical vapor deposition. The low-threshold current density and the high slope efficiency makes this device an attractive active region for the development of single-mode quantum cascade lasers based on third-order-distributed feedback structures. Single-mode, high power was achieved with good continuous and pulsed wave operation.
Highlights
A maximum temperature of 186 K [12]
After a decrease of the differential resistance accompanying the alignment of the injector with the upper state of the laser transition, laser threshold is reached at a current density of 175 A cm−2, accompanied by a very sharp change of slope of the current–voltage characteristics
As shown by the performances reported in figure 6 and as found previously [37], we find that the samples grown by molecular beam epitaxy (MBE) and organometallic chemical vapor deposition (OMCVD) exhibit, for comparable dopings, similar threshold current densities and maximum operating temperatures
Summary
A maximum temperature of 186 K [12]. Even if this last result is a significant improvement compared with the first generation devices, it still lies significantly below the temperatures achievable by thermoelectric cooler based on Peltier effects. The results closest to a final application have been demonstrated in radioastronomy: quantum cascade lasers have been used as local oscillators, pumping a hot electron bolometer and demonstrating a competitive receiver noise temperature [20] Another important step is the report, recently achieved [21], of phase-locking of a THz quantum cascade laser onto a microwave reference. For many of these applications, the challenge is to find a quantum design that offers at the same time a good manufacturability, high wallplug efficiency, and a high maximum operating temperature.
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