Growth Of Gan Films On Gaas (100) Substrate By Rf-Sputtering And E-Beam Evaporation Techniques

Kajian ini menunjukkan penumbuhan lapisan gallium nitrida (GaN) ke atas substrat gallium arsenida (GaAs) berliang melalui kaedah percikan frekuensi radio dan penyejat alur elektron. Sebagai perbandingan, penumbuhan secara terus ke atas substrat GaAs dan lapisan penampan nitrida seperti aluminum nitrida (AlN) dan titanium nitrida (TiN). Pada peringkat pertama kajian ini, parameter yang sesuai untuk menghasilkan GaAs berliang yang berkualiti dengan ketumpatan dan taburan yang seragam telah diperolehi. Didapati bahawa keseragaman dan ketumpatan liang yang tinggi boleh dicapai dengan campuran larutan dimetilformamida (DMF) dan asid sulfurik (H2SO4) dengan kepekatan DMF 75% selama 10 minit, pada ketumpatan arus 250 mA/cm2. Pada peringkat seterusnya, lapisan GaN ditumbuhkan secara berasingan ke atas permukaan yang berbeza melalui percikan frekuensi radio dan penyejat alur elektron. Bukti pengikatan Ga-N di dalam lapisan GaN diperhatikan melalui pengukuran spektroskopi fotoelektron sinar-x (XPS). This work studies the structure, morphology and optical properties of GaN layer grown on porous GaAs/GaAs substrate by radio frequency (RF) sputtering and electron beam (e-beam) evaporation. For comparison, the GaN layer was also grown directly on GaAs substrate and nitride based buffer layers, i.e. aluminum nitride (AlN) and titanium nitride (TiN). In the first part of this work, the best parameters used to obtain good quality porous GaAs on GaAs substrate with uniform distribution and density were determined. It was found that uniform distribution and high density of pores can be fabricated with a mixed solution of dimethylformamide (DMF) and sulphuric acid (H2SO4) with 75% DMF concentration for 10 minutes, at a current density of 250 mA/cm2. In the next stage, the GaN layer was grown separately on different surfaces using RF-sputtering and e-beam evaporation. The evidence of Ga-N bondings inside the GaN layer was observed by XPS measurement

Improvement of Porous GaAs (100) Structure through Electrochemical Etching Based on DMF Solution

We report on the fabrication of porous GaAs (100) using three different acids, H2SO4, HF, and HCl, diluted in DMF based solutions. The mixture of H2SO4 with DMF showed the best porous structures in comparison to other acids. The concentration of the DMF solution was then varied for a fixed concentration of H2SO4. It was apparent that the different concentration of the DMF solvent gave different types of morphology of the porous GaAs. Furthermore, a higher current density improved the uniformity of the pores distribution. The best porous GaAs exhibited well-defined circular shaped pores with high uniformity. To the best of our knowledge, such structure produced in such manner has never been reported so far. Finally, the optimum etching conditions of the pores were proposed

Effect Of Nucleation Time On GaN Layer Grown On Different Shape Of Patterned Sapphire Substrate

This work describes the effect of nucleation time on GaN layer; which was grown separately on three different shape of patterned sapphire substrate (PSS); cone PSS and dome PSS. Prior to the GaN layer growth, a low temperature of GaN nucleation layer was initially grown at 40, 80 and 160 second. The nucleation islands became larger as the nucleation time was longer. Bigger islands promote better coalescence, while smaller islands showed otherwise. Besides, the GaN layer grown on bigger islands exhibit smoother surface. From XRD measurement, FWHM of the GaN peak decreased for longer nucleation time, indicating the benefit of bigger islands to reduce the dislocations in the layer through better coalescence. It was found that the GaN layer grown on dome-patterned substrate exhibits better quality than the one on cone-patterned substrate. The growth of GaN layer on flat sapphire was also performed for comparison

Effect Of Nucleation Time On GaN Layer Grown On Different Shape Of Patterned Sapphire Substrate

This work describes the effect of nucleation time on GaN layer; which was grown separately on three different shape of patterned sapphire substrate (PSS); cone PSS and dome PSS. Prior to the GaN layer growth, a low temperature of GaN nucleation layer was initially grown at 40, 80 and 160 second. The nucleation islands became larger as the nucleation time was longer. Bigger islands promote better coalescence, while smaller islands showed otherwise. Besides, the GaN layer grown on bigger islands exhibit smoother surface. From XRD measurement, FWHM of the GaN peak decreased for longer nucleation time, indicating the benefit of bigger islands to reduce the dislocations in the layer through better coalescence. It was found that the GaN layer grown on dome-patterned substrate exhibits better quality than the one on cone-patterned substrate. The growth of GaN layer on flat sapphire was also performed for comparison

Influence Of Molarity And Time Of Potassium Hydroxide Etching On Al-Rich AlGaN Layer

This work will describe the influence of molarity and time of potassium hydroxide etching on Al-rich AlGaN layer. With potassium hydroxide (KOH) molarity of 5 mol/L, no significant change on the pores formation was observed for 5 and 10 minutes of etching. Nonetheless, there was a possibilty that some of the Ga atoms were eliminated for 10 minutes of etching, resulting in co-existance of AlGaN material with higher Al content. Similar behaviour was also witnessed in the case for 10 mol/L of KOH with 5 and 10 minutes of etching. Nonetheless, well-defined hexagonal patterns were only formed when the etching was conducted using 10 mol/L of KOH for 10 minutes. Such patterns have the potential to increase light extraction efficiency of UV LEDs

Luminescence and Crystalline Properties of InGaN-based LED on Si Substrate with AlN/GaN Superlattice Structure

A crack-free indium gallium nitride (InGaN) based light emitting diode (LED) grown on silicon (Si) substrate was successfully demonstrated by introducing aluminium nitride/gallium nitride (AlN/GaN) superlattice structure (SLS) in the growth of the LED. The luminescence and the crystalline properties of the LED were discussed. From photoluminescence (PL) surface mapping measurement, the emission wavelength of the LED (453 nm) was almost uniform across the LED epi-wafer area. Temperature dependent PL revealed that the dominant emission peak of the LED was 2.77 eV at all temperatures. The emission peak was related to the quantum wells of the LED. Some additional peaks were also observed, in particular at lower temperatures. These peaks were associated to alloy fluctuations in the In0.11Ga0.89N/ In0.02Ga0.98N multiquantum wells (MQWs) of the LED. Furthermore, the dependence of PL intensity and PL decay time on temperature revealed the evidence related to indium and/or interface fluctuations of the quantum wells. From X-ray diffraction (XRD) ω-scan measurements, fringes of the AlN/GaN SLS were clear, indicating the SLS were grown with good interface abruptness. However, the fringes for the MQWs were less uniform, indicating another evidence of the alloy fluctuations in the MQWs. XRD-reciprocal surface mapping (RSM) measurement showed that all epitaxial layers of the LED were grown coherently, and the LED was fully under strain

Fabrication Of Deep Green Light Emitting Diode On Bulk Gallium Nitride Substrate

The indium composition in InxGa1-xN/GaN multi-quantum well structure e(MQW) is crucial because lower indium composition will shift the wavelength towards ultraviolet region. Nevertheless, at certain indium content in MQW, it will out diffuse from the MQW resulting in the wavelength shift from green to much shorter wavelength, after the annealing process for p-type activation. In this study, we had grown a full Light Emitting Diode device with the MQW layer at a relative high temperature for green LED with indium pre-flow at the top of n-type layer just beneath the MQW using Metal Organic Chemical Vapor Deposition (MOCVD). Transmission Electron Microscopy (TEM) image of the MQW prior and post the activation of p-type had been observed, which resulted in good contrast, showing the abruptness of the MQW layer of the device. Homogenous layers of InxGa1- xN/GaN has been observed. We also managed to reduce the wavelength shift of the device significantly. The optical, crystal properties of grown devices had been studied

Effect of indium pre-flow on wavelength shift and crystal structure of deep green light emitting diodes

金沢大学先端科学・社会共創推進機構To produce a deep green (530 nm–570 nm) LED, the suitable indium (In) composition in the InxGa1-xN/GaN multi-quantum well (MQW) structure is crucial because a lower indium composition will shift the wavelength of emission towards the ultraviolet region. In this paper, we clarify the effects of an indium-rich layer to suppress such blue shifting, especially after the annealing process. According to characterizations by the uses of XRD and TEM, narrowing of the MQW layer was observed by the indium capping, while without the capping, the annealing results in a slight narrowing of MQW on the nearest layer to the p-type layer. By adding an indium capping layer, the blue shift of the photoluminescence was also suppressed and a slight red shift to keep green emission was observed. Such photoluminescence properties were consistent with the tiny change of the MQW as seen in the XRD and TEM characterizations

Surface and optical characteristics of polycrystalline GaN layer with different pores profile of porous GaAs/GaAs substrate

This work investigated the influence of pores profile of a porous GaAs/GaAs substrate on surface and optical characteristics of an over-deposited GaN layer. Different pores profile of the porous GaAs/GaAs substrate was introduced by varying the DMF concentration of 50%, 75% and 90%. The pores distribution is more uniform, while the pores size is bigger with higher DMF concentration. In contrast, the pores depth is less deep when the DMF concentration was higher than 75%. Next, the GaN layer was deposited onto the porous GaAs/GaAs substrate using an e-beam evaporator system, followed by thermal annealing in ammonia ambient. It was found that the porous GaAs/GaAs substrate, etched by the DMF concentration above 75% gave lower surface roughness to the polycrystalline GaN layer although the surface morphology showed no significant changes. XRD measurement showed on non-porous substrate favoured hexagonal growth in the polycrystalline GaN layer. Instead, the porous GaAs/GaAs substrate favoured the cubic growth, especially the porous GaAs/GaAs substrate etched by 75% DMF concentration. Moreover, the GaN layer on the porous GaAs/GaAs substrate etched by 75% DMF concentration showed the smallest FWHM of NBE peak emission, while exhibited a relaxation level closer to a reported stress-free bulk GaN, as compared to other samples. After all, the porous GaAs/GaAs substrate, etched by 75% DMF concentration has improved the surface and optical characteristics of the layer due to its better porosity. © 2019 IOP Publishing Ltd

Two-Step GaN Layer Growth for High-Voltage Lateral AlGaN/GaN HEMT

This paper presents reduced dislocation of the AlGaN/GaN heterostructure for high-voltage lateral high-electron-mobility transistor (HEMT) devices. AlGaN/GaN heterostructure was grown on sapphire substrate. Prior to the growth of the AlGaN layer, the GaN layer was grown via two-step growth. In the first step, the V/III ratio was applied at 1902 and then at 3046 in the second step. The FWHMs of the XRD (002) and (102) peaks of the GaN layer were around 205 arcsec ((002) peak) and 277 arcsec ((102) peak). Moreover, the surface of the GaN layer showed clear evidence of step flows, which resulted in the smooth surface of the layer as well as the overgrown of the AlGaN layer. Subsequently, the AlGaN/GaN heterostructure was fabricated into a lateral HEMT with wide gate-to-drain length (LGD). The device exhibited a clear working HEMT characteristic with high breakdown voltages up to 497 V. In comparison to many reported AlGaN/GaN HEMTs, no AlGaN interlayer was inserted in our AlGaN/GaN heterostructure. By improving the growth conditions for the two-step growth, the performance of AlGaN/GaN HEMTs could be improved further