In this work we present the influence of in situ deposited non-continous SiN layer and the chemical precursors III/V mole ratio change during GaN buffer growth for AlGaN/GaN/Si(111) heterostructures with low temperature AlN interlayer on their crystalline quality and electrical mobility of two dimensional electron gas (2DEG). We show, that application of SiN layer resulted in a decrease of (0002) full width at half maximum of diffraction peak below 400 arcsec and build-in stress in 2 µm thick heterostructures below 200 MPa without any relaxation visible on the surface. In optimized AlGaN/GaN heterostructures, by altering V/III mole ratio during growth of GaN subbuffer, the maximum 2DEG mobility of 2057 cm 2 V −1 s −1 , measured by impedance spectroscopy method, was obtained.

In this paper, the combination of using an anti-resonant hollow-core fiber (ARHCF), working as a gas absorption cell, and an inexpensive, commercially available watch quartz tuning fork (QTF), acting as a detector in the quartz-enhanced photothermal spectroscopy (QEPTS) sensor configuration is demonstrated. The proof-of-concept experiment involved the detection of methane (CH4) at 1651 nm (6057 cm−1). The advantage of the high QTF Q-factor combined with a specially designed low-noise amplifier and additional wavelength modulation spectroscopy with the second harmonic (2f-WMS) method of signal analysis, resulted in achieving a normalized noise-equivalent absorption (NNEA) at the level of 1.34 × 10−10 and 2.04 × 10−11 W cm−1 Hz−1/2 for 1 and 100 s of integration time, respectively. Results obtained in that relatively non-complex sensor setup show great potential for further development of cost-optimized and miniaturized gas detectors, taking advantage of the combination of ARHCF-based absorption cells and QTF-aided spectroscopic signal retrieval methods.

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