Jul 11, 2013
Ordered In(Ga)N nanocolumns grown on silicon
The excellent crystal quality of InGaN alloys when grown as nanocolumns (NCs) and their naturally enhanced light extraction (guiding) benefit LED applications. Indeed, the high thermal stability and low droop of NC-based LEDs has been already shown. However, self-assembly grown NCs suffer from a strong morphology dispersion that leads to an inhomogeneous electrical injection and poor/unreliable device performance.
To tackle this issue, selective area growth (SAG) of nitride NCs by plasma assisted molecular beam epitaxy (PAMBE) has been developed, where the substrate is covered by a nanohole Ti mask. The figure above shows a typical SEM image of SAG InGaN/GaN NCs on a silicon substrate, as well as PL spectra of InGaN/GaN samples that can be fabricated to cover the energy range from UV to IR by varying the In content.
The research team (ISOM at Universidad Politecnica of Madrid) has been working on the growth and characterization of nitride nanocolumns since 1997, with special focus on ordered InGaN and GaN nanocolumns during the last 5 years.
Very wide spectral range
Recently, they obtained for the first time ordered In(Ga)N/GaN nanocolumns on cheap, easy to process silicon substrates with emission wavelengths ranging from the ultraviolet to the infrared. In addition, morphology optimized NCs emitting in the green spectral range with an estimated internal quantum efficiency (IQE) of 36% have been achieved on silicon by ISOM. These results pave the way to develop LEDs and detectors based on ordered InGaN structures on Si substrates over a very wide spectral range.
Other research lines currently followed by the team at ISOM are: i) SAG of InGaN and GaN NCs on semi-polar and non-polar substrates; ii) SAG of InGaN/GaN dot-in-a-wire structures; iii) fabrication of high-quality, strain-free GaN and InGaN templates (pseudo-substrates) by NCs coalescence (both non-polar and semi-polar); and iv) SAG of core-shell InGaN/GaN structures by PAMBE.
The researchers published their results in the journal Nanotechnology.
About the author
The study was conducted by researchers from Instituto de Sistemas Optoelectronicos y Microtecnologia (ISOM), which is affiliated to Universidad Politecnica de Madrid (UPM), under a long-standing programme focused on the growth and characterization of III-nitride NCs, in collaboration with the microscopy team at the Paul Drude Institute (PDI) in Berlin. Steven Albert, a PhD student at ISOM-UPM, and Dr Ana Maria Bengoechea-Encabo were responsible for the MBE growth and characterization by photoluminescence, atomic force microscopy, and scanning electron microscopy. Dr Miguel Angel Sanchez-Garcia is Steven Albert’s PhD supervisor, and Prof. Enrique Calleja is group leader. Dr Xiang Kong is a member of the Microstructure department at PDI and Dr Achim Trampert is head of the Microstructure department at PDI.