A. Feduniewicz-Żmuda

InGaN laser diodes operating at 450–460 nm grown by rf-plasma MBEa)

This work demonstrates the first true blue laser diodes (LDs) grown by plasma assisted molecular beam epitaxy that operate at the region of 450–460 nm. The single quantum well LDs were grown on several types of c-plane bulk GaN substrates, with threading dislocation densities varying from 104 to 108cm−2. The key factors that allowed the authors to achieve lasing in true-blue wavelengths are improvements in the growth technology of the InGaN quantum wells attributed to the high nitrogen flux used and the design of the LD structure, which reduced the light losses in the cavity. The authors discuss the influence of the diodes’ design on the parameters of LDs.

Optically pumped GaN∕AlGaN separate-confinement heterostructure laser grown along the (112¯0) nonpolar direction

This letter concerns experiments on optically pumped GaN∕AlGaN separate-confinement heterostructure laser structures grown by plasma assisted molecular beam epitaxy. The structures were grown along the (112¯0) nonpolar crystallographic direction on a bulk GaN substrate. Different widths of GaN quantum wells were applied in the studied structures. Laser action is clearly demonstrated by the spontaneous emission saturation, abrupt line narrowing, and strong TE polarization of output light. A lasing threshold was reached at an excitation power density of 260kW∕cm2 for a 700-μm-long cavity at room temperature.

AlGaN-Free Laser Diodes by Plasma-Assisted Molecular Beam Epitaxy

Room-temperature continuous wave lasing at 432 nm with a threshold current of 7.6 kA/cm2 for nitride-based laser diodes (LDs) grown by plasma-assisted molecular beam epitaxy is reported. The diodes were grown on c-plane GaN substrates with a threading dislocation density of 5×107 cm-2. We used a simplified laser structure design with GaN claddings where the optical modes were confined by the thick 120 nm In0.08Ga0.92N waveguide. Our LDs show a high optical output power of 130 mW, a differential gain of 0.5 W/A, and a lifetime of 50 h.

High quality m-plane GaN grown under nitrogen-rich conditions by plasma assisted molecular beam epitaxya)

Homoepitaxial growth of m-plane GaN (11¯00) as a function of substrate miscut and temperature was studied by plasma assisted molecular beam epitaxy (PAMBE). The authors demonstrate that it is possible to obtain high-quality GaN on the m-plane under nitrogen-rich conditions at 730 °C. This is in contrast to the c-plane where three-dimensional growth mode is observed under the same conditions. They find a strong growth anisotropy and describe GaN (11¯00) surface morphology dependence on the sample miscut direction. The results indicate that by introducing a sample miscut toward ⟨112¯6¯⟩ one may expect parallel atomic steps when growing under nitrogen-rich conditions at 730 °C by PAMBE.

Terahertz 3D printed diffractive lens matrices for field-effect transistor detector focal plane arrays

We present the concept, the fabrication processes and the experimental results for materials and optics that can be used for terahertz field-effect transistor detector focal plane arrays. More specifically, we propose 3D printed arrays of a new type - diffractive multi-zone lenses of which the performance is superior to that of previously used mono-zone diffractive or refractive elements and evaluate them with GaN/AlGaN field-effect transistor terahertz detectors. Experiments performed in the 300-GHz atmospheric window show that the lens arrays offer both a good efficiency and good uniformity, and may improve the signal-to-noise ratio of the terahertz field-effect transistor detectors by more than one order of magnitude. In practice, we tested 3 × 12 lens linear arrays with printed circuit board THz detector arrays used in postal security scanners and observed significant signal-to-noise improvements. Our results clearly show that the proposed technology provides a way to produce cost-effective, reproducible, flat optics for large-size field-effect transistor THz-detector focal plane arrays.

Semipolar (202¯1) GaN laser diodes operating at 388 nm grown by plasma-assisted molecular beam epitaxy

Laser diodes (LDs) were grown by plasma-assisted molecular beam epitaxy on semipolar (202¯1) GaN substrates. Metal-rich conditions provided smooth surface morphology and good structural quality as confirmed by atomic force microscopy and transmission electron microscopy studies. No stacking faults or any linear defects were formed during the growth in the InGaN/InGaN multiquantum well active region. Devices were processed with ridge-waveguide along the [1¯21¯0] direction. Mirrors were cleaved or fabricated by focused ion beam (FIB) processing. LDs operated at 388.2 nm with the threshold current density 13.2 kA/cm2 and the threshold voltage 10.8 V. The device with mirrors fabricated by FIB processing reached practically the same threshold current and slope efficiency as the one with cleaved mirrors. The authors present the beneficial role of the InGaN optical confinement layers in semipolar LDs, which can be optimized to improve the threshold current of these devices.

Broadening of intersubband transitions in InGaN/AlInN multiquantum wells

In this article, the authors report on growth of InGaN/AlInN multiquantum wells (MQWs) by rf-plasma-assisted molecular beam epitaxy on (0001) GaN substrates. Intersubband transitions in InGaN/AlInN MQWs with widths varying from 1.3 to 1.8 nm has been studied experimentally and analyzed theoretically within the electron effective mass approximation. The intersubband absorption between the first and the second electron levels was observed at the wavelength of ∼1.3–1.6 μm. The broadening of intersubband absorption for this system has been found to be much larger than for indium free system (i.e., GaN/AlN MQWs). In addition, it has been found that the broadening increases from ∼280 to ∼390 meV when the nominal quantum well (QW) width decreased from 1.8 to 1.3 nm. On the basis of theoretical calculations combined with the transmission electron microscopy analysis, it has been concluded that the observed broadening of intersubband absorption is due to the QW width fluctuations. It has been estimated that the ma...