Porous GaN Layers Research Articles

Investigation of the effects of porous layer on the electrical properties of Pt/n-GaN Schottky contacts

This article reports the effects of porosity on the enhancement of the Schottky barrier height (SBH) and reduction of the leakage current of Pt Schottky diode based on n-type GaN. The porous GaN layer in this work was generated by electroless chemical etching under UV illumination. For comparative study, two additional samples, i.e. one as-grown sample and one thermally treated sample, were also prepared. The structural studies showed that the porous GaN sample has a relatively rough surface morphology with slightly broader X-ray diffraction peak of the (0 0 0 2) plane. The current–voltage ( I– V) measurements revealed that the electrical characteristics of the Pt Schottky diode were improved significantly by the presence of the porous layer, in which SBH was observed to be enhanced by 27%.

Reduced-stress GaN epitaxial layers grown on Si(1 1 1) by using a porous GaN interlayer converted from GaAs

This paper reports the reduced-stress GaN epitaxial growth on Si (1 1 1) using a porous GaN interlayer which is formed from GaAs layer by a novel nitridation process. Initially a 2 μm thick GaAs layer is grown on a Si(1 1 1) substrate by MBE. Then, a GaN buffer layer of 20 nm thick is grown on the GaAs layer at 550°C in a MOVPE reactor. The GaAs layer capped with the GaN buffer layer is annealed in NH 3 to 1000°C. Through this process, a porous GaN layer is formed beneath the GaN cap layer. An epitaxial GaN layer is grown on the GaN buffer layer at 1000°C in the MOVPE reactor. The epitaxial layer grown on the porous-GaN/Si(1 1 1) structure is found to have no cracks on the surface. In contrast, an epitaxial layer grown on the GaAs layer nitrated without a cap layer many cracks are found in the epilayer and the layer is sometimes peeled off from the substrate. It is found that the surface morphology of the GaN/porous-GaN/Si(1 1 1) sample is markedly improved by employing a 40 nm-thick interlayer grown at 800°C in addition to the above processes. A PL spectrum with a high intensity ratio between the excitonic emission and the deep yellow emission is obtained for the GaN/porous-GaN/Si(1 1 1) sample. E 2 peak position in Raman scattering spectrum also shows a reduced stress for the GaN epilayers grown on the porous-GaN/Si(1 1 1).

Photoconductivity in Porous GaN Layers

The first observation of photoconductivity (PC) in porous GaN layers fabricated by surface anodization of 0.6 μm thick GaN layers grown by HVPE on 6H-SiC substrates is reported. PC was studied at room temperature and a strong photoresponse was observed in anodized GaN layers, whereas no photoconduction in initial (not anodized) epitaxial layers was detected. Both the buildup and the decay of the PC in anodized GaN demonstrated exponential behavior with two time constants of 1.8 and 100 s, respectively. PC spectra of anodized GaN showed a steady increase of the photoresponse as the photon energy was increased from 2.5 to 3 eV. Room and low temperature (15 K) photoluminescence studies were also performed on initial and anodized structures. EBIC measurements showed formation of a barrier on the GaN/SiC interface after anodization. Photoresponse in anodized GaN layers is ascribed to a decrease in carrier concentration in the anodized semiconductor.

Photoconductivity in Porous GaN Layers

Photoconductivity in Porous GaN Layers

Structural characterization and strain relaxation in porous GaN layers

Surface and subsurface structures of porous GaN prepared by anodizing epitaxial GaN layers grown on SiC substrates are investigated by atomic-force microscopy. Comparison of the images of the porous GaN surfaces with those taken on planes cleft perpendicular to the surface shows that the pores are formed along the boundaries of columnar structures of the original GaN films. X-ray investigations show that the porous GaN has less residual stresses than the initial GaN epitaxial layers. Use of porous GaN as a buffer layer for growth of low-stress GaN is proposed.