Blue to true green LEDs with semipolar quantum wells based on GaN nanostripes

Self Cite

This paper reviews our recent investigations about semipolar GaN‐based optoelectronic heterostructures grown on foreign substrates. Two basically different approaches are discussed, both making use of epitaxial growth in the polar c‐direction to minimize any crystalline defects. By selective area growth, stripes with triangular cross‐section have been formed with semipolar side‐facets, on which quantum well and electroluminescence test structures have been deposited. By careful optimisation of many growth parameters, we could drastically increase the growth temperature of GaInN quantum wells emitting beyond 500 nm. In the second approach, the GaN growth starts on inclined sapphire c‐planes, which form the side facets of trenches etched into the substrates. After coalescence, planar semipolar GaN layers can be achieved. We investigated various sapphire wafer orientations leading to {112‾2}, {101‾1}, and {202‾1} layers. After careful optimisation with a major focus on the decrease of the stacking fault density, we have also investigated the doping behaviour of such semipolar structures. Eventually, full electroluminescence test structures could be grown.

Section: Sub‐micrometer Structuresmentioning

confidence: 94%

“…Much better defined structures (Fig. right) have then been obtained by nano‐imprint lithography () and electron beam lithography (). Indeed, even on the side facets of such small stripes having a height of only about 200 nm, semipolar single and double quantum wells were grown ().…”

Section: Sub‐micrometer Structuresmentioning

confidence: 99%

Semipolar GaN‐based heterostructures on foreign substrates

Scholz

Caliebe

Gahramanova

et al. 2015

Self Cite

“…After an undoped spacer, the structure is either planarized with Mg‐doped GaN for LED testing or undoped GaN for optical pumping. Growth conditions can be found in (). The structural and luminescence properties of individual stripes have been directly studied by a one by one correlation of the cathodoluminescence and scanning transmission electron microscopy inside a Tecnai F20 STEM.…”

Section: Methodsmentioning

confidence: 99%

Embedded GaN nanostripes on c‐sapphire for DFB lasers with semipolar quantum wells

Leute

Heinz

Wang

et al. 2015

Self Cite

GaN based laser diodes with semipolar quantum wells are typically grown on free‐standing pseudo‐substrates of small size. We present an approach to create a distributed‐feedback (DFB) laser with semipolar quantum wells (QWs) on c‐oriented templates. The templates are based on 2‐inch sapphire wafers, the method could easily be adapted to larger diameters which are available commercially. GaN nanostripes with triangular cross‐section are grown by selective area epitaxy (SAE) and QWs are grown on their semipolar side facets. The nanostripes are completely embedded and can be sandwiched inside a waveguide. For optical pumping, open waveguide structures with only a bottom cladding are used. Using nanoimprint lithography, stripe masks with 250 nm periodicity were fabricated over the whole wafer area. The periodicity corresponds to a 3rd order DFB structure for a laser emitting in the blue wavelength regime. These samples were analyzed structurally by high‐resolution transmission electron microscopy (HRTEM), and spatio‐spectrally by cathodoluminescence (CL) inside a scanning transmission electron microscope (STEM). Samples with an undoped cap are pumped optically for stimulated emission. To prove the feasibility of realizing a 2nd order DFB structure with this approach, stripes with a 170 nm periodicity are fabricated by electron beam lithography and SAE.

“…In the final step, the active region was capped with p‐doped GaN resulting in a homogeneous and planar surface. Further information on growth conditions and processing can be found in .…”

Section: Sample Growthmentioning

confidence: 99%

Nanoscale cathodoluminescene imaging of III‐nitride‐based LEDs with semipolar quantum wells in a scanning transmission electron microscope

Müller

Schmidt

Metzner

et al. 2015

Self Cite

The optical and crystalline properties of a c‐plane GaN‐based LED structure with embedded semipolar InGaN quantum wells (QW) were investigated using highly spatially resolved cathodoluminescence spectroscopy (CL) directly performed in a scanning transmission electron microscope (STEM). Direct correlation of the cross‐sectional STEM image with the simultaneously recorded spatially resolved CL mapping at room‐temperature reveals the most intense emission coming from the semipolar InGaN QWs. We observe an inhomogeneous wavelength distribution due to local indium fluctuations and varying QW thickness. In contrast, the donor‐acceptor pair recombination (DAP) becomes the dominating luminescence process at 16 K resulting in a superposition of the DAP luminescence and the InGaN QW emission.