Evolution of AlN buffer layers on silicon and effects on the properties of epitaxial GaN films

Abstract

The morphological evolution of AlN buffer layers grown on (111) silicon at high-temperature has been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The structure and morphology of subsequently grown GaN films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. It was found that even though thicker AlN buffer layers are the poor single crystal with some defects like mis-oriented domains, stacking faults, they provide better templates for subsequent growth of GaN films with better crystalline and optical properties, compared to the GaN grown on a thin AlN buffer layer. To prevent the formation of SiN x layers at the interface, TMA was flowed for several seconds prior to the introduction of ammonia into the chamber. The AFM result showed that quasi 2-dimensional growth was quickly achieved for the AlN buffer layer with TMA pre-treatment.

Structural analysis of metalorganic chemical vapor deposited AIN nucleation layers on Si (111)

“…First, we have carried out TEM and AFM measurements to study the micro-structural evolution of AlN nucleation layers without TMA pretreatment [18]. The microstructures of the AlN layer grown for 10 min without such pretreatment exhibited nucleation of three-dimensional islands on the silicon surface.…”

“…With the growth time extended to 80 min, the AlN nuclei covered the whole surface of Si with the average grain size of 120 nm, where poor single crystalline AlN with mis-oriented domains and stacking faults was formed. Also, from cross-sectional TEM, an amorphous SiN x was observed at the interface of the AlN layer and Si [18]. To prevent the formation of amorphous layer at the interface, TMA was allowed to flow for a few seconds before the reaction of TMA and ammonia at high temperature.…”

“…During initial growth stage of AlN, formation of the amorphous SiN x at the interface of AlN and silicon could degrade the quality of AlN and GaN films due to strong Si-N bonding [15][16][17][18]. To prevent the formation of such amorphous layer, some researchers have carried out Al predeposition on the silicon surface during MBE growth of the AlN buffer [19][20][21].…”

Growth of dislocation-free GaN islands on Si(111) using a scandium nitride buffer layer

“…However, the poor lattice match and the difference in thermal expansion coefficients between GaN and Si have hampered the development of high quality, low dislocation-density GaN on silicon. Although AlN is commonly used as a buffer layer to prevent melt-back etching [2] and to reduce the problems of lattice and thermal expansion coefficient mismatch [3,4], its insulating nature prevents back-contacting (particularly as thick AlN buffer layers are needed to obtain crack-free GaN) [5] and the high defect density typically causes large densities of threading dislocations to propagate into the GaN. Other nitride-based buffer layer materials for GaN growth on silicon, such as HfN [6,7] and TiN [8], have also been used, but not for GaN growth using metal-organic vapour-phase epitaxy (MOVPE).…”

Graphene-like AlN layer formation on (111)Si surface by ammonia molecular beam epitaxy

“…An AlN layer is widely used as a buffer layer for the epitaxial growth of III-Nitrides on SiC, Si and Al 2 O 3 substrates [9][10][11][12]. Typically, AlN grows in the wurtzite crystal structure where atoms are fourfold coordinated adopting sp 3 -hybridization with an in-plane constant of 3.11 Å.…”