Henryk Turski

Optically pumped 500 nm InGaN green lasers grown by plasma-assisted molecular beam epitaxy

We report on optically pumped lasing at 500 nm on InGaN laser structures grown by plasma assisted molecular beam epitaxy. The InGaN laser structures were grown under group III-rich conditions on bulk (0001) GaN substrates. The influence of the nitrogen flux and growth temperature on the indium content of InGaN layers was studied. We demonstrate that at elevated growth temperatures, where appreciable dissociation rate for In-N bonds is observed, the indium content of InGaN layers increases with increasing nitrogen flux. We show that growth of InGaN at higher temperatures improves optical quality of InGaN quantum wells, which is crucial for green emitters. The influence of piezoelectric fields on the lasing wavelength is also discussed. In particular, the controversial issue of partial versus complete screening of built-in electric field at lasing conditions is examined, supporting the former case.

Growth mechanism of InGaN by plasma assisted molecular beam epitaxy

In this article, the authors discuss the mechanism of InGaN growth by plasma assisted molecular beam epitaxy. They present the evidence of the influence of substrate miscut on indium incorporation for the growths with different gallium fluxes. They propose and discuss the phenomenological model which describes the incorporation of indium into InGaN layers grown under the indium-rich conditions that takes into account following parameters: gallium and nitrogen fluxes, miscut angle, and the growth temperature.

Nitride-based laser diodes grown by plasma-assisted molecular beam epitaxy

The progress in the growth of nitride-based laser diodes (LDs) made by plasma-assisted molecular beam epitaxy (PAMBE) is reviewed. In this work we describe the GaN and InGaN growth peculiarities, p-type doping efficiency, and the properties of InGaN quantum wells (QWs) grown by PAMBE. We demonstrate continuous wave (cw) LDs operating in the range from 410 to 482 nm. These LDs were grown on low dislocation (0 0 0 1) c-plane bulk GaN substrate, which allow one to fabricate cw LDs with a lifetime exceeding 2000 h. Also, the ultraviolet LDs at 388 nm grown on (2 0 −2 1) semipolar substrates are discussed. The use of high active nitrogen fluxes up to 2 µm/h during the InGaN growth was essential for pushing the lasing wavelengths of PAMBE LDs above 460 nm. Recent advancement of InGaN growth by PAMBE allows one to demonstrate high-quality quantum QWs and excellent morphology for thick layers. We discuss the influence of LDs design on their parameters such as lasing threshold current and laser beam quality.

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.

True-Blue Nitride Laser Diodes Grown by Plasma-Assisted Molecular Beam Epitaxy

We demonstrate true-blue (450–460 nm) nitride-based laser diodes (LDs) grown by plasma-assisted molecular beam epitaxy (PAMBE) on c-plane GaN substrates operating in continuous wave mode. The maximum optical power measured for these LDs is 80 mW, while the lifetime at the optical power of 10 mW is longer than 2000 h. We present a new LD design consisting of a separate confinement heterostructure with GaN claddings and thick In0.08Ga0.92N waveguides. We show that the key element responsible for the improvements in performance of the true-blue PAMBE LDs is the growth of InGaN quantum wells using a high nitrogen flux.

Enhancement of optical confinement factor by InGaN waveguide in blue laser diodes grown by plasma-assisted molecular beam epitaxy

The influence of InxGa1−xN waveguide on the properties of blue (λ = 450 nm) laser diodes grown by plasma-assisted molecular beam epitaxy was studied. The threshold current density was reduced by 50% (to 3.6 kA/cm2) when the indium content was increased from x = 0.04 to 0.08. This is explained by a substantial enhancement of the optical confinement factor for a high-In-content waveguide, which increases the differential modal gain. Furthermore, we observed a decrease in optical losses when Mg-doped layers were separated from the active region by a thicker waveguide. This is attributed to the lower overlap between the optical mode and absorptive Mg-doped layers.

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.

Elimination of leakage of optical modes to GaN substrate in nitride laser diodes using a thick InGaN waveguide

A novel design consisting of a thick InGaN waveguide is proposed to fully eliminate leakage to the GaN substrate in nitride laser diodes. The design is based on the effective refractive index engineering and does not require the commonly used thick AlGaN claddings. The conditions required to fully eliminate the optical leakage are discussed. Experimental results from eight blue laser diodes with different indium contents and thicknesses of the InGaN waveguide grown by plasma-assisted molecular beam epitaxy are presented to validate the theoretical results.

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.

Investigation on the origin of luminescence quenching in N-polar (In,Ga)N multiple quantum wells

The growth of N-polar (In,Ga)N structures by plasma-assisted molecular beam epitaxy is studied. (In,Ga)N multiple quantum well samples with atomically smooth surface were grown and their good structural quality was confirmed by x-ray diffraction, scanning transmission electron microscopy, and defect selective etching. The In incorporation was higher in the N-polar than in the Ga-polar oriented crystal, consistent with previous reports. However, despite the good morphological and structural properties of these samples, no photoluminescence signal from the (In,Ga)N wells was detected. In contrast, a thick N-polar (In,Ga)N layer exhibited a broad peak at 620 nm in good agreement with the In content determined by x-ray diffraction. The potential source of the luminescence quenching in the N-polar (In,Ga)N multiple quantum wells is discussed and attributed either to a strong nonradiative recombination channel at the surface promoted by the electric field or to the high concentration of point defects at the int...