The wear resistance of epitaxial layers of α- and β-polymorphs of gallium oxide grown on sapphire substrates has been considered. This is one of the first studies of the tribological properties of a ...promising wideband semiconductor crystal. As a result of tribotests conducted with the participation of a sapphire counterface in the process of dry friction in air, it has been shown that the layers of a metastable α-Ga
2
O
3
are more resistant to abrasion than the layers of the thermostable β-phase. At the same time, the obtained values of the wear coefficients allow us to attribute both polymorphs to wear-resistant materials and especially α-Ga
2
O
3
with a corundum structure. In addition, α- and β-Ga
2
O
3
demonstrate extremely low values of friction coefficients: lower than those of sapphire.
The elastic and microplastic properties of large quasi-bulk GaN samples of two types, grown by hydride vapor-phase epitaxy, have been acoustically investigated. Samples of the first type are ...polycrystals textured along a crystallographic direction, while second-type samples are single crystals with characteristic V-shaped defects. The results are compared with the data in the literature and analyzed based on the existing theoretical concepts of the influence of dislocations and grain boundaries on the acoustic and mechanical properties of crystals.
Here we report on the growth and characterization of β-Ga2O3 bulk crystals and polycrystalline layer on different substrates. Bulk β-Ga2O3 crystals were produced by free crystallisation of gallium ...oxide melt in sapphire crucible. Transparent single crystals measuring up to 8mm across were obtained. Good structural quality was confirmed by x-ray diffraction rocking curve FWHM values of ~46″. Young’s modulus, shear modulus and hardness of the β-Ga2O3 crystals were measured by nanoindentation and Vickers microindentation techniques. Polycrystalline β-Ga2O3 films were deposited on silicon and sapphire substrates by sublimation method. It was found that structure and morphology of the films were greatly influenced by the material and orientation of the substrates. The best results were achieved on a-plane sapphire substrates where predominantly (111) oriented films were obtained.
•β-Ga2O3 crystals were produced by free crystallization of a melt in Al2O3 crucible.•Elastic and mechanical properties of β-Ga2O3 were measured.•β-Ga2O3 layers were grown by sublimation method on Si and Al2O3 substrates.•Substrate material and orientation define the properties of β-Ga2O3 layers.
•Gallium Oxide (β-Ga2O3) crystals are utilized as substrates for high-power devices.•Thermal annealing was applied to enhance the perfection of bulk (100) β-Ga2O3 crystals.•Annealing led to increase ...in coherent-domain-size value and decrease in domain misorientation.•Annealing led to development a higher stoichiometry and higher crystalline perfection.•Annealing decreased etch pits density 40-fold.
Gallium Oxide is a prospective ultra-wide band-gap semiconductor for high-voltage electronics. Bulk β-Ga2O3 crystals can be utilized as substrates for device structures. The biggest challenge encountered is to grow low defect density wafers with high crystal perfection.
In this work a boule with a diameter of about 20 mm and a height of 20 mm was grown by Czochralski method. The separate plates with dimensions of approx. (10 × 5 × 3)mm3 were cleaved out from the crystal along the (100) cleavage planes.
XRD investigation demonstrated that the crystal is a monoclinic single-phase structure which is characterized by broad rocking curves. The etch pits density revealed by selective wet etching appeared to be high and was estimated as 2 · 107 cm−2. The series of post-growth heat treatments was applied to eliminate these drawbacks. Annealing at 1100 °C during 5 h had the most effect on the crystal structure. Namely, its coherent-domain-size value increased over 400 nm, domain misorientation dropped below the arcminute. The crystal developed higher stoichiometry and higher crystalline perfection. Annealing at the same temperature, but for duration of 11 h dramatically worsen all the parameters of the crystal in combination with its fragmentation in smaller-sized domains. The etch pits density finally decreased 40-fold and took a value of 5 · 105 cm−2.
The microhardness and crack resistance of two main gallium oxide polytypes: metastable α-Ga
2
O
3
with a corundum structure and β-Ga
2
O
3
(high-temperature phase) with a monoclinic crystal ...structure, have been studied using a Vickers method of diamond pyramid indentation. As far as we know, this is the first attempt to compare the mechanical properties of the two polytypes of gallium oxide.
The resistance to deformation and crack formation in epitaxial layers of metastable α- and ε(κ)‑Ga
2
O
3
polymorphs grown on sapphire substrates has been studied by nanoindentation techniques. The ...epilayers of α-Ga
2
O
3
(0001) and ε(κ)-Ga
2
O
3
(001) polymorphs are characterized by hardness
H
(18.7 and 17.5 GPa) and Young’s modulus
E
(283.4 and 256.1 GPa), respectively. It is established that the critical stress intensity factor (characterizing the cracking resistance) for ε(κ)-Ga
2
O
3
is
K
1
c
∼ 0.67 MPa m
1/2
and that for α-Ga
2
O
3
is
K
1
c
∼ 0.70 MPa m
1/2
.
Record thick (up to 100 μm) epitaxial layers of a prospective metastable semiconductor Ga
2
O
3
were grown by HVPE (Halide Vapor Phase Epitaxy) on GaN buffer layers on
c
-sapphire substrates. The ...X-ray diffraction pattern of the layers show that the structure of the layer is a pure κ(ε)-Ga
2
O
3
without any other phases. At the same time, the organization of a domain structure was observed, which manifests itself in the form of pseudohexagonal prisms that retain the orientation of the gallium nitride sublayer. Schottky diodes with nickel contacts were fabricated and the electrical and photoelectric properties of the layers were studied. Capacitance–voltage (
C
–
V
) and frequency–capacitance (
C
–
f
) dependencies were studied, photocurrent and photocapacitance spectra were measured.
Epitaxial layers of a new wide-band semiconductor (α-Ga
2
O
3
doped with tin) have been grown by chloride epitaxy on smooth and patterned substrates, which are widely used to increase the emission ...yield in high-efficiency LED structures based on InGaN, and studied. The properties of the obtained gallium-oxide layers have been compared. Both types of samples had
n
-type conductivity, but the frequency and voltage dependences of their capacitance differed. Differences in the dislocation structure of epitaxial α-Ga
2
O
3
layers on smooth and patterned substrates have been identified by X-ray diffractometry.
The tribological experiment applied to the gallium oxide wafer led to changes in its structure which can reduce the single crystal perfection. The effect of mechanical wear on the subsurface layers ...of the β-Ga2O3 single crystal wafers applied to the (2‾01) plane is studied. A decrease in crystallinity within a mosaic structure appearing in the worn samples is revealed with a help of ω-scan analysis, performed by XRD. SEM analysis of the wear track relief of the worn samples showed an emergence of the lamellas framed by domain walls as a result of single crystal splitting.
The reactive stresses induced in Ni
49
Fe
18
Ga
27
Co
6
-alloy single crystals during martensitic transformations with a limited possibility of shape-memory-strain recovery have been experimentally ...studied. The data on these crystals are compared with the results obtained previously for Cu–Al–Ni, Ni–Ti, and Ni‒Fe–Ga crystals. The potential of application of the Ni
49
Fe
18
Ga
27
Co
6
single crystals in designing drives and power motors is demonstrated.
