Tall-barrier terahertz quantum cascade lasers

Abstract

Thermally activated leakage current in high-performance short-wavelength quantum cascade lasers

Simulating terahertz quantum cascade lasers: Trends from samples from different labs

“…4(d) KhanalOE2015, an indirect design, does not fit into the picture. While the other indirect designs have barriers with x ¼ 0.25, this device has a lower barrier height (x ¼ 0.15), which may provide substantial leakage into the continuum 22 for the high electric field required for indirect designs. This is not taken into account in the NEGF model and could explain why the model provides a smaller peak current.…”

“…This is in turn based on a VBO of 0:53x eV, assumed temperature independent, as well as low temperature results for the band gaps of both GaAs and AlAs. This relation for the conduction band offset is however seldom used in the QCL community, 22,25,26 where instead a lower offset is often preferred. This might be more reasonable for the design of structures aimed at high temperature operation, where we expect the band gap to decrease.…”

“…Here, it is well-known that the reproduction of devices from different groups frequently provided different results, where the origin is far from understood, see, e.g., Ref. 22. It is also known that the samples grown at the same lab but under different growth campaigns can differ, although methods now exist to guarantee run-to-run reproducibility.…”

Room temperature negative differential resistance in terahertz quantum cascade laser structures

“…However, despite the expectation for a major breakthrough by reducing the TA-LTC, to-date no significant improvement in temperature performance has been achieved by increasing the barriers height in THz-QCL devices. [4][5][6] Here, motivated by this inconsistency between the theoretical expectations and the actual performance of highbarrier devices, we study highly diagonal GaAs/Al 0.30 GaAsbased THz-QCLs and analyze the physical mechanisms that affect their temperature performance. Based on the analysis, we designed a new THz-QCL structure with low leakage at room temperature as manifested by the measured negative differential resistance (NDR).…”

“…3 Based on this study, barriers higher than 15% aluminum concentration would be beneficial to reduce this leakage channel. [4][5][6] Going forward, the combination of highly diagonal structures and higher barriers should significantly reduce both the TA-LOP scattering and TA-LTC. 3 This expected behavior is illustrated in Figure 1 with the calculations of output power dependence on temperature for a highly diagonal THz-QCL in the two limiting cases of including or excluding the TA-LTC, respectively.…”