Design and fabrication of enhanced lateral growth for dislocation reduction in GaN using nanodashes

Abstract

The semiconductor gallium nitride is the material at the centre of energy-efficient solid-state lighting and is becoming increasingly important in high-power and high-frequency electronics. Reducing the dislocation density of gallium nitride planar layers is important for improving the performance and reliability of devices, such as light-emitting diodes and high-electron-mobility transistors. The patterning of selective growth masks is one technique for forcing a three-dimensional growth mode in order to control the propagation of threading defects to the active device layers. The morphology of the three-dimensional growth front is determined by the relative growth rates of the different facets that are formed, and for GaN is typically limited by the slow-growing {1 −1 0 1} facets. We demonstrate how the introduction of nanodash growth windows can be oriented in an array to preserve fast-growing {1 1 −2 2} facets at the early stage of growth to accelerate coalescence of three-dimensional structures into a continuous GaN layer. Cathodoluminescence and Electron Channelling Contrast Imaging methods, both used to measure the threading dislocation density, reveal that the dislocations are organised and form a distinctive pattern according to the underlying mask. By optimising the arrangement of nanodashes and the nanodash density, the threading dislocation density of GaN on sapphire epilayers can be reduced significantly from 109 cm−2 to 3.0 × 107 cm−2. Raman spectroscopy, used to monitor the strain in the overgrown GaN epilayers, shows that the position of the GaN E2H phonon mode peak was reduced as the dash density increases for a sample grown via pendeo-epitaxy whilst no obvious change was recorded for a sample grown via more conventional epitaxial lateral overgrowth. These results show how growth mask design can be used to circumvent limitations imposed by the growth dynamics. Moreover, they have revealed a greater understanding of the influence of the growth process on the dislocation density which will lead to higher performing electronic and optoelectronic devices as a result of the lower dislocation densities achieved

Imaging basal plane stacking faults and dislocations in (11-22) GaN using electron channelling contrast imaging

“…34,35 A. Imaging of TDs in (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) In ECCI, individual vertical TDs appear as spots with black-white (B-W) contrast, 36 and this is shown in the expanded excerpt of Fig. 3, highlighted by a solid circle.…”

“…Sample description and growth of the semi-polar GaN thin film A single layer (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) semi-polar GaN template with a thickness of 1300 nm was grown on m-plane sapphire using a high temperature AlN buffer by metal organic chemical vapour deposition (MOCVD). Mask-patterned micro-rod arrays were then fabricated on the (11-22) GaN template for subsequent overgrowth.…”

“…40 In order to visualise and maximise the contrast associated with stacking faults, one has to choose the condition g. R ¼ 0 or an integer. 41 In the case of plan-view TEM imaging of BSFs in (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN, generally, the specimen is tilted to %32…”

“…1 An encouraging alternative to reduce polarization effects is the use of non-polar and semi-polar orientations where the projection of the polarization vector along the growth axis is zero or is smaller than in the case of the c-plane orientation. 2,3 Semi-polar planes recently investigated are the (10-11), (10)(11)(12)(13), (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), and (20)(21) planes. The (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) plane is of particular interest due to this plane's surface leading to easier accommodation of the larger indium atoms when compared to the polar (0001), non-polar and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and other semi-polar planes.…”

“…[22][23][24][25] In this work, we demonstrate the application of ECCI to image BSFs in semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN and determine the conditions to maximise the channelling contrast to reveal the BSFs and TDs in different scattering geometries. We have chosen semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) as an example to validate the applicability of using ECCI to characterise BSFs and also due to this material's potential commercial importance especially for long wavelength light emitters. 12,26 Nonetheless, the ECCI technique can also be adopted for other semi-polar orientations, as long as the appropriate channelling (diffraction) conditions are chosen.…”