**3.4.2 AlN films on fianite substrates**

The AlN films on fianite substrates were grown using MOGPE technique. The AlxGa1-xN direct gap semiconductors are very useful in the development of UV photodetectors. By altering Al content in GaN-based solid solutions, it is possible to obtain the material with a forbidden band ranging in 3.43-6.2 eV thus covering 200-365 nm spectral band. This spectral band is of practical importance in UV astronomy, ozone layer monitoring, combustion and water sensors. These films are both of original interest, as well as are useful as nucleating and buffer layers in GaN epitaxy.

Growth of the films was started from thin 20-50 nm nucleating layer. Two growth modes were used: at 650 С with subsequent annealing in ammonia-hydrogen media at 1100 С during 30 min followed by growing-up of the basic layer and high-temperature growth of AlN at the same temperature. Before the deposition of AlN films the fianite substrates were annealed in pure hydrogen at ~1070ОС. Mirror-flat homogeneous AlN films with the roughness not exceeding 0.6 nm (Fig .14) were deposited on (100) and (111) fianite substrates.

Layer-by-layer analysis of AlN nucleating layer on the fianite substrates was carried out by SIMS using TOF SIMS-5 device (sputtering by Cs+, 2 keV, 250 х 250 raster, negative recording mode, Bi+ probe beam 25 keV).

Fig. 14. Interference microscope image (Interference microscope "Talysurf") of surface (а) and surface relief (b); and layer-by-layer secondary ion mass-spectrometry (c) of low temperature AlN seeding layer on fianite substrate.

epitaxial growth. Traces of the polycrystalline phase at 32.4 (suggested 0.1-1.0 intensity

The AlN films on fianite substrates were grown using MOGPE technique. The AlxGa1-xN direct gap semiconductors are very useful in the development of UV photodetectors. By altering Al content in GaN-based solid solutions, it is possible to obtain the material with a forbidden band ranging in 3.43-6.2 eV thus covering 200-365 nm spectral band. This spectral band is of practical importance in UV astronomy, ozone layer monitoring, combustion and water sensors. These films are both of original interest, as well as are useful as nucleating

Growth of the films was started from thin 20-50 nm nucleating layer. Two growth modes were used: at 650 С with subsequent annealing in ammonia-hydrogen media at 1100 С during 30 min followed by growing-up of the basic layer and high-temperature growth of AlN at the same temperature. Before the deposition of AlN films the fianite substrates were annealed in pure hydrogen at ~1070ОС. Mirror-flat homogeneous AlN films with the roughness not exceeding 0.6 nm (Fig .14) were deposited on (100) and (111) fianite

Layer-by-layer analysis of AlN nucleating layer on the fianite substrates was carried out by SIMS using TOF SIMS-5 device (sputtering by Cs+, 2 keV, 250 х 250 raster, negative

0 100 200 300 400 500

 C 18O Al AlN N3 Zr ZrO

Cs+ 2keV

Sputtering time, s

c Fig. 14. Interference microscope image (Interference microscope "Talysurf") of surface (а) and surface relief (b); and layer-by-layer secondary ion mass-spectrometry (c) of low

a b

100

temperature AlN seeding layer on fianite substrate.

101

102

Intensity, cps

103

104

H1005B1 AlN/ZrO2

units) were not detected.

**3.4.2 AlN films on fianite substrates**

and buffer layers in GaN epitaxy.

recording mode, Bi+ probe beam 25 keV).

substrates.

The study has shown that the layers had uniform distribution of its constituents, the concentration profile of Zr atoms at the hetero-interface being very sharp (Fig. 14c). The use of AlN nucleating layers on the fianite buffering layers allows deposition of continuous and homogeneous GaN layers of hexagonal modification.

#### **3.4.3 Electrically active defects in GaN films on GaAs substrates with fianite buffer layers**

Comparative study of density and electric activity of structural defects in the GaN epitaxial films grown on GaAs substrates with various buffer layers were carried out by **Induced bias technique**. Induced bias (IBT) technique has been developed rather recently [30, 31]. It is contact-free similarity of induced current technique (EBICmode). IBT is nondestructive contact-free diagnostic technique of semiconducting materials and microelectronic devices. IBT is based on detecting of voltage (or charge) generated by an electron probe of scanning electron microscope (SEM). Draft-scheme is shown in Fig. 15 a.

Fig. 15. Outline of induced potential method (a) and scanning electron microscope images of electrically active polygonal defects in GaAs films: secondary-electron emission mode (b); b - induced potential mode (c).

The electron probe (e) scans the surface of a crystal under the study (O). Metal ring (D), in which surface charge generated by electrons through capacitive coupling is induced, is a detector of the signal. The signal from the ring electrode is monitored in the SEM display (or by other measurement equipment) through charge-sensitive amplifier (PA) (Fig. 15 a). The technique allows qualitative monitoring of semiconductor plates, structures and devices identifying electric active inhomogeneities such as dislocations, stacking faults, microfractures, extent of doping by various dopants, all *p-n* junctions and Schottky barriers, etc (see for example Fig. 15 b,c). Quantitative measurements of local fundamental characteristics of semiconductors are also possible (diffusion distance, nonequilibrium carrier lifetime, its surface recombination rate, diffusion barrier height).

The studies have shown that the use of GaAs substrates with porous GaAs layer resulted in a decrease of the electric activity of structural defects in the GaN films and in an increase of its electrical uniformity as compared to GaN films grown on monolithic GaAs substrates. The use of GaAs substrates with double buffer layer (fianite on porous GaAs) allows additionally decreasing concentration of the electrically active defects in the GaN films to more than an order of magnitude (Fig. 16).

Fianite in Photonics 153

101

Fig. 17. Layer-by-layer secondary ion mass-spectrometry of GaN/fianite/por(mono)Si/Si

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

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

In recent years a considerable attention was drawn to fianite films on silicon due to its electric and optic device applications, such as isolating layers in SOI (silicon-on-insulator) devices [32], gate dielectric in Si- [33, 34], SiGe- [35] and AIIIBV -based [36] device structures, buffer layers for producing of optic coatings of films of various semiconductors [37–40],

layers: porous GaAs) (1) and double buffer –fianite on porous GaAs (2).

**4. Functional fianite films on Si, Ge and GaAs substrates** 

**4.1 Techniques for deposition of fianite films on Si and GaAs substrates** 

102

103

Intensity, cps

104

0 400 800 1200 1600 2000

Sputtering time, s

rastr 400\*400mkm 1stage/GaN

0 200 400 600 800

Sputtering time, s

rastr 200\*200mkm 2stage/GaN-substrate GaAs

 Ga2 N As

101

102

103

Intensity, cps

104

**/porGaAs/GaAs**

**GaN/ZrO2**

 Ga2 N As

0 200 400 600 800 1000 1200 1400

(a) and GaN/fianite/porGaAs/GaAs (b) structures.

Sputtering time, s

/por(mono)Si/Si

rastr 300\*300mkm

a b

10<sup>2</sup>

10<sup>3</sup>

Intensity, cps

10<sup>4</sup>

10<sup>5</sup>

N843 GaN/ZrO2

hexagonal modification.

superconductors [41-43], ferroelectrics, etc.

 Si mono Si por

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).
