Migration characterization of Ga and In adatoms on dielectric surface in selective MOVPE

Abstract

Migration characterizations of Ga and In adatoms on the dielectric surface in selective metal organic vapor phase epitaxy (MOVPE) were investigated. In the typical MOVPE environment, the selectivity of growth is preserved for GaN, and the growth rate of GaN micro-pyramids is sensitive to the period of the patterned SiO2 mask. A surface migration induced model was adopted to figure out the effective migration length of Ga adatoms on the dielectric surface. Different from the growth of GaN, the selective area growth of InGaN on the patterned template would induce the deposition of InGaN polycrystalline particles on the patterned SiO2 mask with a long period. It was demonstrated with a scanning electron microscope and energy dispersive spectroscopy that the In adatoms exhibit a shorter migration length on the dielectric surface.

New measurement method of displacement susceptibility based on time‐domain current and potential combined spectra

“…Displacement susceptibility (χ ∞ ) is able to be used to quantitatively characterise the displacement polarisation, which occurs in any dielectric [1]. According to the Debye equation, complex permittivity contains the displacement and relaxation components, but the traditional dielectric spectrum method cannot distinguish them from each other [2], which makes it difficult to study the displacement and relaxation polarisation.…”

“…Many microscopic models (e.g., atomic model [3] and density-functional theory [4]) are able to calculate the displacement susceptibility, which is a bit different from the measurement one due to the idealisation and simplification of these models. According to the dielectric physics, for the non-ferromagnetic dielectrics, the high frequency permittivity (ε ∞ ) is equal to the square of refractive index (n), that is, ε ∞ = n 2 [1]. As the displacement susceptibility is equal to the high frequency permittivity minus one, that is, χ ∞ = ε ∞ −1, the measurement of the refractive index via optical method (OM) can determine the displacement susceptibility.…”

“…Takada et al proposed a dc integrated charge method to obtain the relationship between the charge amount and time by integrating the current flowing through a capacitor, which is in series with the sample, and evaluated the permittivity according to the initial charge amount (time = 4 s) [10,11]. However, this initial time is much larger than the settling time (10 −15 -10 −16 s) of displacement polarisation [1], so the dc integrated charge method is hardly capable of determining the displacement susceptibility.…”

Influence of adatom migration on wrinkling morphologies of AlGaN/GaN micro-pyramids grown by selective MOVPE

“…Therefore, the hexagonal AlGaN micro-pyramid prepared by selective area growth (SAG) technique is thought as a kind of promising building block for reducing the TD [9,10] and suppressing the undesirable polarization effect. [11,12] Although high quality GaN pyramid has been successfully realized by SAG technology in a metal-organicvapor phase epitaxy (MOVPE) system, [13][14][15] the SAG of Al-GaN pyramids has been a challenge so far because Al adatoms cannot diffuse along a long distance and it is easy to form the nucleation of AlGaN spontaneously on dielectric surface in the environment of nitrogen due to the high bond energy of Al-N. [16] Thus, it is difficult to realize a hexagonal Al-GaN micro-pyramid at the mask openings grown by selective area MOVPE, particularly for the high Al composition. But, it may be feasible to form AlGaN/GaN hexagonal pyramidal structure when growing an AlGaN capping layer on a GaN pyramid.…”