We demonstrate a stack of two III-nitride laser diodes (LDs) interconnected by a tunnel junction grown by plasma-assisted molecular beam epitaxy. Hydrogen-free growth is used to obtain as-grown ...p-type conductivity essential for buried tunnel junctions (TJ). We show the impact of the design of tunnel junction. In particular, we show that, apart from the beneficial piezoelectric polarization inside the TJ, heavy doping reduces the differential resistivity even further. The device starts to lase at a wavelength of 459 nm with a slope efficiency (SE) of 0.7 W/A followed by lasing at 456 nm from the second active region doubling the total SE to 1.4 W/A. This demonstration opens new possibilities for the fabrication of stacks of ultraviolet and visible high power pulsed III-nitride LD.
We report on III-nitride-based micro-light-emitting diodes (µLEDs) operating at 450 nm wavelength with diameters down to 2 µm. Devices with a standard LED structure followed by a tunnel junction were ...grown by plasma-assisted molecular beam epitaxy. The emission size of µLEDs was defined by shallow He + implantation of the tunnel junction region. The ion implantation process allows to create flat devices, applicable to further epitaxial regrowth. The shift of current density for the maximum external quantum efficiency as a function of µLEDs diameter was observed. This effect may be a fingerprint of the change in the external efficiency related to the lateral carrier diffusion (limited by holes) in InGaN quantum wells.
In good agreement with measurements, self-consistent numerical simulations are utilized to analyze internal device physics, performance limitations, and optimization options for a unique laser design ...with multiple active regions separated by tunnel junctions, featuring surprisingly wide InGaN quantum wells. Contrary to common assumptions, these quantum wells are revealed to allow for perfect screening of the strong built-in polarization field, while optical gain is provided by higher quantum levels. However, internal absorption, low p-cladding conductivity, and self-heating are shown to strongly limit the laser performance.
In this paper, we demonstrate a novel approach utilizing tunnel junction (TJ) to realize GaN-based distributed feedback (DFB) laser diodes (LDs). Thanks to the use of the TJ the top metal contact is ...moved to the side of the ridge and the DFB grating is placed directly on top of the ridge. The high refractive index contrast between air and GaN, together with the high overlap of optical mode with the grating, provides a high coupling coefficient. The demonstrated DFB LD operates at λ=450.15 nm with a side mode suppression ratio higher than 35dB. The results are compared to a standard Fabry-Perot LD.
In this work we study the peculiar role of gallium and nitrogen atoms in the growth of InGaN by Plasma Assisted Molecular Beam Epitaxy (PAMBE). We investigate growth of InGaN layers on vicinal GaN ...(0001) substrates. Indium incorporation as a function of gallium and nitrogen fluxes was examined. We propose a microscopic model of InGaN growth by PAMBE postulating different indium adatom incorporation mechanisms on two nonequivalent atomic step edges of wurtzite crystal. The role of gallium and nitrogen fluxes during the growth of InGaN layers is discussed.
► Indium incorporation limits in plasma assisted molecular beam epitaxy. ► Phenomenological model of In incorporation into InGaN layers. ► InGaN morphology affected by presence of non-equivalent atomic step edges. ► The role of nitrogen flux in the growth of high indium content InGaN.
Semipolar (202̅1), nonpolar m-plane (101̅0) and polar c-plane (0001) GaN and InGaN layers were grown by plasma-assisted molecular beam epitaxy. The surface of semipolar and nonpolar GaN grown under ...Ga-rich conditions is very smooth. The indium incorporation efficiency in InGaN layers grown under In-rich growth conditions is studied on three surface orientations (i) as a function of temperature from 570 to 650°C and (ii) for varied active nitrogen flux from 0.41 to 2.03µm/h. The In content follows the relation (101̅0)<(202̅1) <<(0001) in all of the experiments. Indium composition in InGaN layers can be increased (i) by the decrease of the growth temperature and (ii) increase of the applied nitrogen flux for all studied surface orientations. Additionally, surface morphology of semipolar, nonpolar and c-polar InGaN layers grown at 650, 640 and 620°C is compared. No increase in surface roughness for semipolar and nonpolar InGaN was observed in contrast to c-plane counterparts.
•Semipolar, nonpolar and c-plane GaN and InGaN layers were grown by PAMBE.•The indium incorporation efficiency follows the relation (101̅0)<(202̅1)<<(0001).•For all studied surface orientations In content is increased at low growth temperature.•In content is increased for higher applied nitrogen flux.•Smooth surface of semipolar and nonopolar GaN and InGaN is obtained.
It is shown that in polar InGaN QWs emitting in the blue-green spectral region a Stokes shift between spontaneous emission (SE) and optical transition observed in contactless electroreflectance (CER) ...spectrum (absorption-like technique) can be observed even at room temperature, despite the fact that the SE is not associated with localized states. Time resolved photoluminescence measurements clearly confirm that the SE is strongly localized at low temperatures whereas at room temperature the carrier localization disappears and the SE can be attributed to the fundamental transition in this QW. The Stokes shift is observed in this QW system because of the large built-in electric field, i.e., the CER transition is a superposition of all optical transitions with non-zero electron-hole overlap integrals and, therefore, the energy of this transition does not correspond to the fundamental transition of InGaN QW. Lasing from this QW has been observed at the wavelength of 475 nm, whereas the SE was observed at 500 nm. The 25 nm shift between the lasing and SE is observed because of a screening of the built-in electric field by photogenerated carriers. However, our analysis shows that the built-in electric field inside the InGaN QW region is not fully screened under the lasing conditions.
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