Multiple GaInN quantum wells (QWs) were grown on facets with reduced piezoelectric fields (PFs) of selectively grown GaN stripes oriented along the ⟨11¯00⟩ and ⟨112¯0⟩ directions by metalorganic vapor phase epitaxy. We found a higher normalized growth rate for the GaInN QWs on the {11¯01} facets compared to the {112¯2} facets and the planar grown reference sample on unstructured template. The different luminescence wavelengths observed for the QWs on these different facets can partly be explained by the reduced PFs, but additionally indicate that the In incorporation efficiency depends on the facet type. On stripes with trapezoidal cross section, we found strong interfacet migration of In and Ga changing the local thickness and composition significantly.
The authors demonstrate the fabrication and evaluation of bright semipolar GaInN∕GaN blue light emitting diodes (LEDs). The structures are realized by growing five GaInN∕GaN quantum wells on the {11¯01} side facets of selectively grown n-GaN stripes with triangular shape running along the ⟨112¯0⟩ direction covered with a Mg-doped GaN top layer. The growth was done by metal organic vapor phase epitaxy using a conventional [0001] sapphire substrate. The devices have circular mesa structures with diameters between 70 and 140μm. Continuous wave on-wafer optical output powers as high as 700μW and 3mW could be achieved under dc conditions for 20 and 110mA, respectively. The current dependent blueshift of the peak emission wavelength caused by screening effects of the piezoelectric field was only 1.5nm for currents between 1 and 50mA. This is less than half the value measured on c-plane LEDs and confirms the reduced piezoelectric field in our LED structures.
Direction and strength of piezoelectric built-in fields of GaInN quantum wells have been experimentally determined. The quantum wells have been grown either on the conventional {0001} crystal plane of GaN or on {11¯01} facets of selectively grown GaN stripes. The emission peak position of the electric-field-dependent photoluminescence can be modeled and yields value and sign of the piezoelectric field dependent on the strain of the quantum wells. On the semipolar {11¯01} facets, the quantum wells show a much weaker field (−0.1MV∕cm) compared to quantum wells grown on polar {0001} planes (−1.9MV∕cm), consistent with theoretic predictions.
GaInN quantum wells with reduced piezoelectric field deposited epitaxially on the {11¯01} facets of selectively grown GaN stripes show distinct polarization properties of the emitted light. Systematic electro- and photoluminescence studies demonstrate that the light is linearly polarized parallel to the stripes, representing the ⟨112¯0⟩ direction of the GaN crystal. Our model calculations show that this is a consequence of the strain-induced valence-band splitting depending on the crystal orientation. The polarization ratio is calculated and compared to measured values.
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