The mobility limited by cluster scattering in ternary alloy semiconductor quantum wire （QWR） is theoretically inves- tigated under Born approximation. We calculate the screened mobility due to clusters （high indium composition lnGaN） scattering in the InxGal_xN QWR structure. The characteristics of the cluster scattering mechanism are discussed in terms of the indium composition of clusters, the one-dimensional electron gas （1DEG） concentration, and the radius of QWR. We find that the density, breadth of cluster, and the correlation length have a strong effect on the electron mobility due to cluster scattering, Finally, a comparison of the cluster scattering is made with the alloy-disorder scattering. It is found that the cluster scattering acts as a significant scattering event to impact the resultant electron mobility in ternary alloy QWR.
The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in AlxGa1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the AlxGa1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.
By using x-ray diffraction analysis,we investigate the major structural parameters such as strain state and crystal quality of non-polar a-plane In_(x)𝑦Ga_(1−x)𝑦N thin films grown on r-sapphire substrates by metalorganic chemical vapour deposition.The results of the inplane grazing incidence diffraction technique are analyzed and compared with a complementary out-of-plane high resolution x-ray diffraction technique.When the indium composition is low,the a-plane In_(x)𝑦Ga_(1−x)𝑦N layer is tensile strain in the growth direction(𝑏a-axis)and compressive strain in the two in-plane directions(𝑛a-axis and𝑑a-axis).The strain status becomes contrary when the indium composition is high.The stress in the𝑛a-axis direction𝜏σyy is larger than that in the a-axis directionσzz.Furthermore,strain in the two in-plane directions decrease and the crystal quality becomes better with the growing of the In_(x)Ga_(1−z)N film.
Three main technologies for bulk GaN growth, i.e., hydride vapor phase epitaxy （HVPE）, Na-flux method, and am- monothermal method, are discussed. We report our recent work in HVPE growth of GaN substrate, including dislocation reduction, strain control, separation, and doping of GaN film. The growth mechanisms of GaN by Na-flux and ammonother- mal methods are compared with those of HVPE. The mechanical behaviors of dislocation in bulk GaN are investigated through nano-indentation and high-space resolution surface photo-voltage spectroscopy. In the last part, the progress in growing some devices on GaN substrate by homo-epitaxy is introduced.
AIN thick films were grown on c-plane sapphire substrates by hydride vapor phase epitaxy at high temperature. The evolution of the strain state and crystal quality of AIN with increase of thickness were investigated by transmission electron microscopy, field-emission scanning electron microscopy, Raman spectra and atomic force microscopy （AFM）. As the thickness increased, the stress in the epilayers decreased gradually, which was attributed to the reaction of dislocations at the first several microns in thickness. When the thickness was more than 20 μm, the stress was almost fully relaxed due to the formation of cracks. Wet etching experiments indicated that the dislocation density decreased with the increase of thickness. The AFM images showed that the density of dark spots on the surface obviously decreased and the atomic steps became straight as the thickness increased.
An altemative way is proposed to interpret I-V characteristics of GalnP single-junction solar cells by position-dependent leakage ofphotocurrent. With this approach, the I-V curves of solar cells under non-uniform illumination are well analyzed. The effective spreading resistance is also extracted to understand the dynamic behavior of between the open-circuit voltage and short-circuit current points. The conditions under which the one- diode model will fail are addressed in detail. These analyses are also applicable for a characterization of the I-V curves with lateral voltage distribution under uniform illumination.
The aluminum incorporation efficiencies in nonpolar A-plane and polar C-plane A1GaN films grown by metalorganic vapour phase epitaxy （MOVPE） are investigated. It is found that the aluminum content in A-plane A1GaN film is obviously higher than that in the C-plane sample when the growth temperature is above 1070 ℃. The high aluminum incorporation efficiency is beneficial to fabricating deep ultraviolet optoelectronic devices. Moreover, the influences of the gas inlet ratio, the V/Ⅲ ratio, and the chamber pressure on the aluminum content are studied. The results are important for growing the A1GaN films, especially nonpolar A1GaN epilayers.
