Abstract:We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement … Show more
“…The analysis was done over a 90 • range with an interval of 30 • , where 0 • and 90 • correspond to directions [1123] and [1100], respectively. It is noted that the XRC FWHM for all samples along [1100] is broader than [1123], which are similar to the reported observations on (1122) GaN [18,[26][27][28]. For example, [1123] and [1100] planes of sample S1 shown to have the FWHM of 464 and 1390 arcsec, respectively.…”
Section: Resultssupporting
confidence: 82%
“…In addition, a diffuse scattering (DS) streak parallel to [0001] direction can be seen in all samples. It has been reported that the DS steak is correlated with the presence of BSFs and PDs[18,36]. A shorter DS streak was observed in S4 compared to S1, indicating a reduction in BSFs and PDs as the flux rate decreases, which agrees with the on-axis result.…”
supporting
confidence: 86%
“…On the flip side, semi-polar (1122) GaN, for example, suffers from high defect density; 98% is contributed by partial dislocations (PDs) and basal stacking faults (BSFs), and 2% is caused by a-type perfect dislocations [14,15]. Numerous efforts, such as epitaxial lateral overgrowth (ELOG) [16], AlN/GaN multilayer, silicon nitride (SiN x ) interlayer [17], double AlN or GaN nucleation layers [18], patterned sapphire substrates [19] and graded superlattices [20] have been explored to solve this problem to achieve an enhanced crystal quality and surface morphology. Growth parameters, such as temperature [21], V/III ratio [22] and reactor pressure [23,24], have been widely discussed to understand the influence of the growth process.…”
We report on the crystal improvement of semi-polar (112¯2) gallium nitride epitaxy layer on m-plane (101¯0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower flux rate enhanced the crystal quality of GaN epitaxy with the lowest FWHM values of 394 and 1173 arc seconds at [11¯23] and [11¯00] planes, respectively. In addition, Raman spectroscopy showed that flux rate did not affect the stress state of the GaN crystal. However, atomic force microscopy (AFM) micrograph depicted an anomalous trend where the lowest flux rate produces roughest surface with RMS roughness of 40.41 nm. Further analysis of AFM results on the undulation period length along [11¯23] and [11¯00] directions is carried out. It shows that as the growth rate decreases, the average undulation period along [11¯23] and [11¯00] directions increases from 2.59 µm and 1.90 µm to 3.52 µm and 3.52 µm, respectively. The mechanism for the surface roughening at the lower flux rate is then explained by using the adatom surface diffusion relation L ~ Dτ.
“…The analysis was done over a 90 • range with an interval of 30 • , where 0 • and 90 • correspond to directions [1123] and [1100], respectively. It is noted that the XRC FWHM for all samples along [1100] is broader than [1123], which are similar to the reported observations on (1122) GaN [18,[26][27][28]. For example, [1123] and [1100] planes of sample S1 shown to have the FWHM of 464 and 1390 arcsec, respectively.…”
Section: Resultssupporting
confidence: 82%
“…In addition, a diffuse scattering (DS) streak parallel to [0001] direction can be seen in all samples. It has been reported that the DS steak is correlated with the presence of BSFs and PDs[18,36]. A shorter DS streak was observed in S4 compared to S1, indicating a reduction in BSFs and PDs as the flux rate decreases, which agrees with the on-axis result.…”
supporting
confidence: 86%
“…On the flip side, semi-polar (1122) GaN, for example, suffers from high defect density; 98% is contributed by partial dislocations (PDs) and basal stacking faults (BSFs), and 2% is caused by a-type perfect dislocations [14,15]. Numerous efforts, such as epitaxial lateral overgrowth (ELOG) [16], AlN/GaN multilayer, silicon nitride (SiN x ) interlayer [17], double AlN or GaN nucleation layers [18], patterned sapphire substrates [19] and graded superlattices [20] have been explored to solve this problem to achieve an enhanced crystal quality and surface morphology. Growth parameters, such as temperature [21], V/III ratio [22] and reactor pressure [23,24], have been widely discussed to understand the influence of the growth process.…”
We report on the crystal improvement of semi-polar (112¯2) gallium nitride epitaxy layer on m-plane (101¯0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower flux rate enhanced the crystal quality of GaN epitaxy with the lowest FWHM values of 394 and 1173 arc seconds at [11¯23] and [11¯00] planes, respectively. In addition, Raman spectroscopy showed that flux rate did not affect the stress state of the GaN crystal. However, atomic force microscopy (AFM) micrograph depicted an anomalous trend where the lowest flux rate produces roughest surface with RMS roughness of 40.41 nm. Further analysis of AFM results on the undulation period length along [11¯23] and [11¯00] directions is carried out. It shows that as the growth rate decreases, the average undulation period along [11¯23] and [11¯00] directions increases from 2.59 µm and 1.90 µm to 3.52 µm and 3.52 µm, respectively. The mechanism for the surface roughening at the lower flux rate is then explained by using the adatom surface diffusion relation L ~ Dτ.
“…It is noteworthy that the stripe-like and arrowhead structures were generated from asymmetric lattice mismatches of 16.1% and 1.1% between the substrate and a- GaN film along the [1–100] and [0002] directions, respectively 25 . This result could be attributed to the different probabilities for surface atom incorporation and diffusion lengths along these non-identical crystallographic directions 26 . Figure 2 Surface structure images for samples S1, S2, S3 and S4: optical microscope images at 20 times magnification: ( a – d ), respectively; FESEM surface images: ( e – h ), respectively; and AFM images: ( i – l ), respectively.…”
We demonstrated high-quality single crystalline a-plane undoped-gallium nitride grown on a nonpatterned r-plane sapphire substrate via metal–organic chemical vapor deposition. The effect of four different numbers of sandwiched strain-periodic AlN/GaN multilayers on the strain state, crystal quality, optical and electrical properties was investigated. Field emission scanning electron microscopy and atomic force microscopy showed that the surface morphology was improved upon insertion of 120 pairs of AlN/GaN thin layers with a root-mean-square roughness of 2.15 nm. On-axis X-ray ω-scan rocking curves showed enhanced crystalline quality: the full width at half maximum decreased from 1224 to 756 arcsec along the [0001] direction and from 2628 to 1360 arcsec along the [1–100] direction for a-GaN grown with 120 pairs of AlN/GaN compared to a-GaN without AlN/GaN pairs. Reciprocal space mapping showed that a-plane GaN with a high number of AlN/GaN pairs exhibits near-relaxation strain states. Room-temperature photoluminescence spectra showed that the sample with the highest number of AlN/GaN pairs exhibited the lowest-intensity yellow and blue luminescence bands, indicating a reduction in defects and dislocations. The a-plane InGaN/GaN LEDs with 120 pairs of SSPM-L AlN/GaN exhibited a significant increase (~ 250%) in light output power compared to that of LEDs without SSPM-L AlN/GaN pairs.
“…As for the structural properties, HR-XRD phase analysis was utilized by majority of the research groups within the selected article, whereas XRC and RSM analyses were the least to be reported. On-and off-XRC and RSM analyses were reported to investigate defects and/or dislocations and the strain/stress, respectively [2,3,31,66,75]. It should be noted that the highest crystal qualities as investigated via XRC analysis were 300 and 325 arcsec along [23,30].…”
Ultraviolet photodetectors have been widely utilized in several applications, such as advanced communication, ozone sensing, air purification, flame detection, etc. Gallium nitride and its compound semiconductors have been promising candidates in photodetection applications. Unlike polar gallium nitride-based optoelectronics, non-polar gallium nitride-based optoelectronics have gained huge attention due to the piezoelectric and spontaneous polarization effect–induced quantum confined-stark effect being eliminated. In turn, non-polar gallium nitride-based photodetectors portray higher efficiency and faster response compared to the polar growth direction. To date, however, a systematic literature review of non-polar gallium nitride-based photodetectors has yet to be demonstrated. Hence, the objective of this systematic literature review is to critically analyze the data related to non-polar gallium nitride-based photodetectors. Based on the pool of literature, three categories are introduced, namely, growth and fabrication, electrical properties, and structural, morphological, and optical properties. In addition, bibliometric analysis, a precise open-source tool, was used to conduct a comprehensive science mapping analysis of non-polar gallium nitride-based photodetectors. Finally, challenges, motivations, and future opportunities of non-polar gallium nitride-based photodetectors are presented. The future opportunities of non-polar GaN-based photodetectors in terms of growth conditions, fabrication, and characterization are also presented. This systematic literature review can provide initial reading material for researchers and industries working on non-polar gallium nitride-based photodetectors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
