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Sensor miniaturization together with broadening temperature sensing range are fundamental challenges in nanothermometry. By exploiting a large temperature-dependent screening effect observed in a resonant tunneling diode in sequence with a GaInNAs/GaAs quantum well, we present a low dimensional, wide range, and high sensitive nanothermometer. This sensor shows a large threshold voltage shift of the bistable switching of more than 4.5 V for a temperature raise from 4.5 to 295 K, with a linear voltage–temperature response of 19.2 mV K–1, and a temperature uncertainty in the millikelvin (mK) range. Also, when we monitor the electroluminescence emission spectrum, an optical read-out control of the thermometer is provided. The combination of electrical and optical read-outs together with the sensor architecture excel the device as a thermometer with the capability of noninvasive temperature sensing, high local resolution, and sensitivity.

Studying cavity quantum electrodynamical effects is an emerging and important field of research for the understanding of the many body quantum theory as well as for the generation of a new type of efficient lasers. Here we report a dramatic change in the photon statistics of quantum dot based micropillar lasers where a finite fraction of the emission is reflected back into the microcavity after a roundtrip time in an external cavity, where greatly exceeds the coherence time. Photon bunching was observed above the threshold current where the second order autocorrelation function g(2)() at zero-lag can reach values up to 3.51±0.06. The change in the photon statistics of the two non-degenerated fundamental modes were found to be correlated, indicating non-trivial interactions between both cavity modes. Furthermore the optical feedback led to revivals of the bunching signal in integer multiples of the round trip time of the external cavity and to a decrease in the coherence time of the laser. These phenomena compare well with milliwatt chaotic lasers induced by an external feedback, indicating that chaos might occur in the nanowatt lasing regime where fluctuations in the photon statistics are in the leading order.

We present investigations on the coherence of the emission from the fundamental mode of an AlGaInAs/GaAs quantum-dot microcavity laser. We measure the first-order field-correlation function g^(1)(τ) with a Michelson interferometer, from which we determine coherence times of up to 20?ns for the highest pump powers. To fully characterize the coherence properties of the cavity emission, we apply a phenomenological model that connects the first- and second-order correlation functions. Hereby it is possible to overcome the limited sensitivity of the streak camera used for photon-correlation measurements, and thus to extend the accessible excitation-power range for g^(2)(τ) down to the thermal regime.

There are two particularly promising approaches to reach laser emission in the 3.0 - 3.5 m wavelength range with application grade performance; GaSb based laser structures using GaInAsSb / AlGaInAsSb type-I quantum well (QW) active region, as well as type-II interband cascade (IC) material have been investigated and corresponding results are discussed in this paper. We also present different techniques for the fabrication of spectrally monomode distributed feedback (DFB) lasers for sensing applications in the targeted wavelength range. Based on the different waveguide designs of the two material approaches, different concepts to achieve monomode emission were applied: lateral metal gratings were used for type-I laser structures, vertical sidewall gratings for ICL designs. The fabrication procedure, including growth of the laser structures by molecular beam epitaxy, device processing and characterization, are described in the following. DFB emission under continuous wave (cw) operation was achieved up to room temperature (RT) in the target wavelength range. Sidemode suppression ratios (SMSRs) exceed 30dB for the fabricated devices and mode-hop free monomode tuning ranges of several nanometers are demonstrated.