**3.4.4 GaN films on Si and GaAs substrates with fianite buffer layers**

Silicon and gallium arsenide are promising substrates for GaN and other AIIIN epitaxy due to its high quality, large dimensions and a low net-cost, as well as possibility to integrate GaN-based devices with high-developed silicon and gallium arsenide electronics and opto electronics. However, there are three considerable problems occurring at GaN epitaxy: first, a significant parameter mismatch of GaN layer and Si or GaAs substrates, second, difference of thermal expansion coefficients of the layer and substrates and third, insufficient chemical and thermal stability of the substrates at the epitaxy temperature. Application of various buffer layers, in particular, fianite-based, can be an efficient method for solution of the above problems.

GaN epitaxial films were grown by MOGPE technique using capillary epitaxy on Si and GaAs substrates with various buffer layers. Tri-methylgallium (TMG), arsin (AsH3) and ammonia (NH3) were used as Ga, As and N sources, respectively. **Single** (fianite, layer of porous Si or GaAs material) and **double** (fianite on porous Si and GaAs) were tested. The first "prominent" porous buffer layer was suggested to allow decreasing thermoelastic strains in the second heteroepitaxial buffer thus improving its morphology and structure. The upper buffer layer, being chemically stable in the growth medium, provides fine matching with the working heteroepitaxial layer.

The epitaxial structures grown were studied using various techniques: photoluminescence (PL), scanning electron microscopy under induced current (IC) and induced bias conditions and secondary-ion mass spectroscopy (SIMS).

It was established that the use of fianite buffer layer on Si substrate prevents formation of amorphous silicon nitride. The GaN films grown on Si substrates with fianite buffer layer were of hexagonal modification (-GaN) and had mosaic single crystal structure. It was established that the use of porous Si in the complex fianite/Si buffer allows improving of adhesion of GaN layer and its uniformity by phase composition and thickness.

Layerwise SIMS analysis of the GaN films grown on Si and GaAs substrates with fianite buffer layers has shown that the fianite layer serve as a barrier for diffusion of silicon and arsenium into GaN film from Si and GaAs substrates, respectively (Fig. 17). Good insulating properties of ZrO2 in double buffer give some possibility to use the technology "Semiconductor on dielectric" which is promising to improve the integration level.

a b

Silicon and gallium arsenide are promising substrates for GaN and other AIIIN epitaxy due to its high quality, large dimensions and a low net-cost, as well as possibility to integrate GaN-based devices with high-developed silicon and gallium arsenide electronics and opto electronics. However, there are three considerable problems occurring at GaN epitaxy: first, a significant parameter mismatch of GaN layer and Si or GaAs substrates, second, difference of thermal expansion coefficients of the layer and substrates and third, insufficient chemical and thermal stability of the substrates at the epitaxy temperature. Application of various buffer layers, in particular, fianite-based, can be an efficient method for solution of the above

GaN epitaxial films were grown by MOGPE technique using capillary epitaxy on Si and GaAs substrates with various buffer layers. Tri-methylgallium (TMG), arsin (AsH3) and ammonia (NH3) were used as Ga, As and N sources, respectively. **Single** (fianite, layer of porous Si or GaAs material) and **double** (fianite on porous Si and GaAs) were tested. The first "prominent" porous buffer layer was suggested to allow decreasing thermoelastic strains in the second heteroepitaxial buffer thus improving its morphology and structure. The upper buffer layer, being chemically stable in the growth medium, provides fine

The epitaxial structures grown were studied using various techniques: photoluminescence (PL), scanning electron microscopy under induced current (IC) and induced bias conditions

It was established that the use of fianite buffer layer on Si substrate prevents formation of amorphous silicon nitride. The GaN films grown on Si substrates with fianite buffer layer were of hexagonal modification (-GaN) and had mosaic single crystal structure. It was established that the use of porous Si in the complex fianite/Si buffer allows improving of

Layerwise SIMS analysis of the GaN films grown on Si and GaAs substrates with fianite buffer layers has shown that the fianite layer serve as a barrier for diffusion of silicon and arsenium into GaN film from Si and GaAs substrates, respectively (Fig. 17). Good insulating properties of ZrO2 in double buffer give some possibility to use the technology

adhesion of GaN layer and its uniformity by phase composition and thickness.

"Semiconductor on dielectric" which is promising to improve the integration level.

Fig. 16. Electrically active defects in GaN film on GaAs substrate with buffer layers:

а — single buffer (fianite); b — double buffer (fianite on porous GaAs).

**3.4.4 GaN films on Si and GaAs substrates with fianite buffer layers** 

matching with the working heteroepitaxial layer.

and secondary-ion mass spectroscopy (SIMS).

problems.

Fig. 17. Layer-by-layer secondary ion mass-spectrometry of GaN/fianite/por(mono)Si/Si (a) and GaN/fianite/porGaAs/GaAs (b) structures.

Comparative studies of PL spectra recorded at 300ОК of GaN films grown on a monolithic GaAs substrate and GaAs substrates with various kinds of buffer layers have been carried out (Fig. 18): 1 – single buffer "porous GaAs"; 2 – double buffer "fianite on porous GaAs"

Fig. 18. Photoluminescence spectra of GaN films (300ОК) on GaAs substrate with buffer layers: porous GaAs) (1) and double buffer –fianite on porous GaAs (2).

The position of PL peaks in the spectra corresponded to characteristic peak of cubic GaN. Consequently, the use of the single buffer layer of porous GaAs, as well as double buffer layer (fianite on porous GaAs) allows growing GaN films of cubic modification. The growth of GaN film grown on monolithic GaAs substrate in contrast resulted to formation of hexagonal modification.
