6 μm thick crack-free GaN on silicon substrate
Abstract
Epitaxial growth of GaN on silicon is usually accompanied by dense networks of micro-cracks which is a major obstacle for GaN device processing. The insertion of low-temperature AlN (LT-AlN) stress-compensating interlayers has been proven to overcome the cracking problem. Using this approach, we present crack-free GaN on silicon (111) of more than 6.5µm in thickness grown by MOVPE. Such a multi-layer stack consists of an AlN nucleation layer, 100nm AlGaN, a SiN interlayer, and finally, 1.5µm GaN followed by four periods of LT-AlN and 1.3µm GaN. The microscopic properties of the crack-free, nominally undoped GaN are analyzed by highly spatially and spectrally resolved cathodoluminescence microscopy (CL), proving a material quality comparable to GaN on sapphire. Along the growth direction we find an abrupt improvement of the optical properties after each of the LT-AlN interlayers: Above the SiN the GaN emission appears with a FWHM>20meV, nevertheless, the uppermost GaN layer emits sharp excitonic lines with FWHM=3meV for the dominant (D^0X) at T=6K. The high lateral homogeneity of the (D^0X) position (standard deviation σ=0.6meV for 55µm x 35µm) is consistent with a width of the x-ray rocking curve of the (0002) reflex of 180arcsec. The impact of the Al-rich layers on the evolution of stress is directly visualized in cross-sectional CL. Growth on the SiN/AlGaN leads to an initial compressive stress in GaN. While each of the individual GaN layers exhibits a gradient towards tensile stress, the accumulated stress is always partially compensated by the following LT-AlN. Thus, after 6.5µm GaN growth we find an average (D^0X) emission energy of 3.466eV, i.e. only 0.2GPa tensile stress at the sample surface.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2003
- Bibcode:
- 2003APS..MAR.J1121R