High Quality GaN Layers on Si(111) Substrates: AlN Buffer Layer Optimisation and Insertion of a SiN Intermediate Layer

Abstract

We present a study on the material properties of GaN films grown on (111) silicon substrates by low-pressure metalorganic chemical vapour deposition using AlN buffer layers. This buffer layer is optimised with respect to growth temperature and time for the optical and structural properties of the GaN epilayers. The insertion of a Si x N y intermediate layer significantly increases the optical and structural properties. It results in a reduction of the D 0 X FWHM to 10 meV and in a 2.5-fold increase of its luminescence intensity. The FWHM of symmetric and asymmetric w-scans are reduced from 832 to 669 arcsec and from 702 to 547 arcsec, respectively.Introduction Despite difficulties in the growth of GaN on silicon, caused by a lattice mismatch of 17% and by thermal expansion coefficient incompatibility, silicon is considered to be one of the best candidates as an alternative, inexpensive and large substrate for depositing GaN. Future applications, like the integration of silicon based electronics with GaN opto-electronic devices, are the motivation for this research. Because GaN cannot be used as a buffer layer on Si(111) substrates due to wetting problems, we have investigated the use of AlN buffer layers. We have optimised the AlN buffer layer with respect to its thickness and growth temperature. The physical properties of MOCVD grown GaN epilayers (layer thicknesses %3 mm) on Si(111) substrates with these AlN buffer layers were investigated. Alternatively, we propose the insertion of a SiN intermediate layer after 1 mm of GaN growth. The results of this alternative approach will be compared with those obtained with the AlN buffer.

The influence of nitridation time on the structural properties of GaN grown on Si (111) substrate

“…The mosaic structure of the epilayers is determined by the size and angular distribution of the mosaic blocks. The vertical and lateral correlation lengths, heterogeneous strain, and degree of mosaicity as expressed by the tilt and twist angles are important parameters in characterizing the quality of the epitaxial films with a large lattice mismatch to the substrate [17,19,22]. The mosaic blocks are assumed to be slightly misoriented with respect to each other.…”

“…Due to a large lattice mismatch, a high density of threading dislocations on the order of (10 9 -10 10 cm −2 ) exists in the GaN film on silicon substrates, which significantly affects the performance of the GaN based devices [8]. In order to obtain crack-free highquality GaN film on Si substrate, various types of buffer layers and growth conditions as well as post-growth heat treatment processes have been proposed by different research groups [10][11][12][13][14][15][16][17]. However, the appearance of the cracks is quite random on the film, which produces significant difficulty in device applications.…”

“…With a similar approach, a double-buffer structure of AlN/Si x N y was used to obtain high quality GaN film on Si substrate by using molecular beam epitaxy (MBE) [16]. The singlecrystalline SiN x was obtained by introducing the active nitrogen plasma to the Si (111) surface at 900°C for approximately 30 s. Hageman et al [17] reported significant improvements on the optical and structural properties of the 1 μm GaN layer with the creation of a SiN x intermediate layer.…”

The electrical, optical, and structural properties of GaN epitaxial layers grown on Si(111) substrate with interlayers

“…Also large lattice mismatch causes high density of threading dislocations on the order of (10 9 cm −2 -10 10 cm −2 ) in the GaN film on silicon substrates, which significantly limits the performance of GaN based devices [8]. Different research groups have proposed various types of growth conditions and buffer layers as well as post-growth heat treatment processes in order to obtain crack-free high-quality GaN film on Si substrate [10][11][12][13][14][15][16]. But, the appearance of the cracks is quite random on the film, which produces significant difficulty in device applications.…”

“…Also, Hageman et al [16] reported significant improvements in the optical and structural properties of the 1 µm GaN layer with the creation of an SiN x buffer layer.…”