In-k Seo

Characteristics of UV photodetector fabricated by Al0.3Ga0.7N/GaN heterostructure

Abstract We report on the solar-blind metal–semiconductor–metal (MSM) UV photodetector fabricated on the Al 0.3 Ga 0.7 N/GaN heterostructure layer grown on sapphire(0xa00xa00xa01) by metalorganic chemical vapor deposition. The use of high-temperature (HT)-AlN interlayer in Al 0.3 Ga 0.7 N/GaN epilayer and its effects on the grown structures were explored. The Al 0.3 Ga 0.7 N-based interdigitated MSM photodetector has been successfully fabricated and characterized. The device reveals that a visible rejection is more than 3 orders of magnitude with a cutoff wavelength at 292xa0nm and the responsivity is up to 0.15xa0A/W. Also, MSM UV photodetector shows very fast response time of 12.5xa0ns without reverse bias and very low dark current due to low noise with a typical value of 72xa0pA and 0.15xa0μA at 10 and 40xa0V, respectively. The obtained results are very promising for the enhancement of solar-blind MSM UV photodetectors and simultaneously very sufficient for application in UV region such as UV astronomy, UV missile detection and visible blindness materials.

Characteristics of GaN/Si(1 1 1) epitaxy grown using Al0.1Ga0.9N/AlN composite nucleation layers having different thicknesses of AlN

Abstract We have studied the effects of Al 0.1 Ga 0.9 N(150xa0nm)/AlN composite nucleation layers (CNLs) having different thicknesses of AlN ranging from 20 to 41xa0nm on the growth characteristics of GaN/Si(1xa01xa01) epitaxy. The surface morphology of the GaN epitaxial layers which were grown on Al 0.1 Ga 0.9 N(150xa0nm)/AlN CNLs showed that the number of thermal etch pits and cracks were abruptly decreased with the increase of AlN thickness from 20 to 35xa0nm. However, the morphology of GaN epitaxy which was grown on Al 0.1 Ga 0.9 N(150xa0nm)/AlN CNL having AlN of thickness 41xa0nm above 35xa0nm showed that the number of etch pits increased again. The GaN/Si(1xa01xa01) epitaxy grown by using Al 0.1 Ga 0.9 N(150xa0nm)/AlN(35xa0nm) CNL showed that the highest crystallinity having a FWHM of 1157xa0arcsec for the (0xa00xa00xa02) diffraction. Photoluminescence (PL) spectrum at room temperature for GaN/Si(1xa01xa01) epitaxy grown using Al 0.1 Ga 0.9 N(150xa0nm)/AlN(35xa0nm) CNL showed sharp band edge emission at 364xa0nm, which do not have yellow luminescence related to various defects such as vacancy and dislocation. The PL spectra at room temperature for the GaN layers grown using other CNLs showed yellow luminescence at around 580xa0nm in addition to the band edge emission. Moreover, the FWHM of the main exitonic peak at 10xa0K for the GaN/Si(1xa01xa01) epitaxy, which was grown using Al 0.1 Ga 0.9 N(150xa0nm)/AlN(35xa0nm) CNL, has the lowest value of 12.81xa0meV. It is obvious that the Al 0.1 Ga 0.9 N(150xa0nm)/AlN CNL having suitable thickness of AlN plays an important role in improving the crystallinity and optical properties of GaN/Si(1xa01xa01) heteroepitaxy without showing any defects such as pits and cracks over the surface by reducing the mismatch of thermal expansion coefficient and lattice constant between GaN and Si(1xa01xa01) compared with other nucleation layer such as Al x Ga 1− x N or AlN alone.

The role of AlN buffer layer in AlxGa1-xN/GaN heterostructures with x from 0.35 to 0.5 grown on sapphire (0 0 0 1)

Abstract We report the role of a thin AlN buffer layer introduced between Al x Ga 1− x N and GaN grown on sapphire (0xa00xa00xa01) by MOVPE. The heterostructures have high x values ranging from 0.35 to 0.50. After growing the 20xa0nm thick AlN buffer layer on GaN/sapphire (0xa00xa00xa01) epitaxy, the 1.0xa0μm thick Al x Ga 1− x N epitaxial layers were grown by increasing the flow rate of TMA. The measured Al mole fractions of Al x Ga 1− x N/GaN heteroepitaxy grown using the thin AlN buffer from each TCD rocking curve are 0.35, 0.37, 0.45 and 0.50, respectively. As the incorporation rate of Al in the Al x Ga 1− x N increases, the crystallinity is improving and the RMS values scanned by AFM of their surfaces become lower. The optoelectronic characteristics of these heteroepitaxial layers were evaluated by cathodoluminescence and found to improve with the increase of x . To the contrary these trends of improvement, it is usually known that the properties such as crystallinity, surface morphology and optical properties of the Al x Ga 1− x N/GaN heteroepitaxial layers grown without AlN buffer layer become worse with the increase of x above 0.2. The electrical resistivities of Al 0.35 Ga 0.65 N/GaN, Al 0.37 Ga 0.63 N/GaN, Al 0.45 Ga 0.55 N/GaN and Al 0.5 Ga 0.5 N/GaN heterostructure, which were grown with the thin AlN buffer, measured by four point probing method are 13.5, 18.1, 31.7 and 36.2 MΩxa0cm, respectively. The resisitivity increases with the raising of x . It may be caused by the increment of the intrinsic own-resistance.

Characteristics of GaN/Si(111) Epitaxy Grown using Al0.1Ga0.9N/AlN Composite Nucleation Layers having Different Thicknesses of AlN

We have studied the effects of Al 0.1 Ga 0.9 N(150 nm)/AlN Composite Nucleation Layers (CNLs) having different thicknesses of AlN ranging from 20 to 41 nm on the growth characteristics of GaN/Si(111) epitaxy. The surface morphologies of the GaN epitaxial layers which were grown on Al 0.1 Ga 0.9 N(150nm)/AlN CNLs showed that the number of thermal etch pits and cracks was abruptly decreased with the increase of AlN thickness from 20 to 35 nm. However, the morphology of GaN epitaxy which was grown on Al 0.1 Ga 0.9 N(150 nm)/AlN CNL having AlN of 41 nm thick above 35 nm showed that the number of them was increased again. So, the GaN/Si(111) epitaxy which was grown using Al 0.1 Ga 0.9 N(150 nm)/AlN(35 nm) CNL showed the highest crystallinity having the FWHM of 1157 arcsec for the (0002) diffraction. Photoluminescence spectrum at room temperature for GaN/Si(111) epitaxy grown using Al 0.1 Ga 0.9 N(150 nm)/AlN(35 nm) CNL showed a sharp band edge emission at 364 nm, which especially doesnt have yellow luminescence related to various defects such as vacancy and dislocation. Meanwhile, the spectra at room temperature for the others showed yellow luminescence at around 580 nm except each band edge emission. Moreover, the FWHM of main exitonic peak at 10 K for the GaN/Si(111) epitaxy which was grown using Al 0.1 Ga 0.9 N(150 nm)/AlN(35 nm) CNL is the lowest value of 12.81 meV among them. It is obvious that the Al 0.1 Ga 0.9 N(150 nm)/AlN CNL having suitable thickness of AlN plays an important role in improving the crystallinity and optical properties of GaN/Si(111) heteroepitaxy without any defects such as pits and cracks over the surface by reducing the mismatch of thermal expansion coefficient and lattice constant between GaN and Si(111) comparing with AlxGa1-xN or AlN nucleation layer alone.