Sven Scholz

Ultrawide electrical tuning of light matter interaction in a high electron mobility transistor structure

The interaction between intersubband resonances (ISRs) and metamaterial microcavities constitutes a strongly coupled system where new resonances form that depend on the coupling strength. Here we present experimental evidence of strong coupling between the cavity resonance of a terahertz metamaterial and the ISR in a high electron mobility transistor (HEMT) structure. The device is electrically switched from an uncoupled to a strongly coupled regime by tuning the ISR with epitaxially grown transparent gate. The asymmetric potential in the HEMT structure enables ultrawide electrical tuning of ISR, which is an order of magnitude higher as compared to an equivalent square well. For a single heterojunction with a triangular confinement, we achieve an avoided splitting of 0.52 THz, which is a significant fraction of the bare intersubband resonance at 2 THz.

Spectral modification of the laser emission of a terahertz quantum cascade laser induced by broad-band double pulse injection seeding

We demonstrate by injection seeding that the spectral emission of a terahertz (THz) quantum cascade laser (QCL) can be modified with broad-band THz pulses whose bandwidths are greater than the QCL bandwidth. Two broad-band THz pulses delayed in time imprint a modulation on the single THz pulse spectrum. The resulting spectrum is used to injection seed the THz QCL. By varying the time delay between the THz pulses, the amplitude distribution of the QCL longitudinal modes is modified. By applying this approach, the QCL emission is reversibly switched from multi-mode to single mode emission.

Laplace deep level transient spectroscopy on self-assembled quantum dots

Self-assembled InAs quantum dots in a GaAs matrix are studied by Laplace deep level transient spectroscopy (LDLTS). This technique is demonstrated to be complementary to the well-established capacitance spectroscopy concepts and is particularly well suited for characterization of quantum dot layers with large separations from conductive layers. In comparison to conventional deep level transient spectroscopy, LDLTS can also be applied in the tunneling regime where the lifetimes of the confined states are independent of temperature, while in the thermal regime, LDLTS has a superior selectivity. The problems encountered hitherto with this technique are demonstrated to originate from the ill-posed character of the inverse Laplace transform and can be solved by a properly adapted choice of the regularization parameter.