Kazuhiro Kuwahara

INFLUENCES OF INITIAL NITRIDATION AND BUFFER LAYER DEPOSITION ON THE MORPHOLOGY OF A (0001) GAN LAYER GROWN ON SAPPHIRE SUBSTRATES

Hexagonal GaN is grown on (0001) sapphire substrates using an atmospheric pressure organometallic vapor phase epitaxy method. We investigate the influences of the initial treatment of sapphire substrate, such as initial nitridation and low-temperature GaN buffer layer deposition, upon the surface morphology and crystallinity. The thermal stability of grown GaN layers is also investigated using a thermal etching process in a H2 atmosphere in order to obtain the information concerning the surface polarity of GaN(0001) layers. When sapphire substrates are initially nitrided, highly crystalline GaN layers with large hexagonal facets are obtained and its surface appears to be (0001)N. On the other hand, the deposition of a thicker buffer layer on the nitrided sapphire substrates improves the surface morphology, and the surface polarity of the mirror surface appears to be (0001)Ga. The initial nitridation of sapphire substrates and the GaN buffer layer deposition are considered to be important processes from vi...

Reduction of threading dislocations by InGaAs interlayer in GaAs layers grown on Si substrates

High-quality GaAs epilayers with dislocation densities of 1.2×106 cm−2 on (100)Si substrates have been obtained by insertion of an InGaAs strained interlayer combined with thermal cycle annealing instead of strained layer superlattices. All the layers were grown by low-pressure metalorganic vapor phase epitaxy. The threading dislocation density near the surface of 4 μm thick GaAs was measured by plan-view transmission electron microscopy. The threading dislocation density was found to be very sensitive to the In composition of the interlayer and the specifics of thermal cycle annealing.

Two-step growth of InP on GaAs substrates by metalorganic vapor phase epitaxy

Layers of InP grown on GaAs substrates by a two-step growth using metalorganic vapor phase epitaxy have been investigated. We have succeeded in improving the crystallinity of InP epilayers on GaAs substrates by employing a low V/III ratio for initial layer growth. The initial layers of InP were characterized by transmission electron microscopy. By lowering the V/III ratio to 20 during the growth of initial layers at 400°C, the surface became smooth and the X-ray diffraction peak intensity increased. The full width at half maximum of X-ray rocking curve is as small as 163 arcsec for a 3 μm InP layer. Using a low V/III ratio for initial layer growth is effective in improving the crystallinity of InP epilayers.

Substrate effect on the deposition of Zn3P2 thin films prepared by a hot‐wall method

Zn3P2 thin films have been deposited by a hot‐wall method on Pyrex glass and (100)GaAs substrates. For GaAs crystalline substrates, higher deposition rates were obtained at the same source and substrate temperatures than those for glass substrates. Layers deposited on (100) GaAs substrates showed stronger preferential (004)orientation of the tetragonal structure, and hence an improved columnar structure is obtained as compared with those on glass substrates. The films having higher crystalline quality deposited on GaAs substrates have room‐temperature resistivities as low as ∼10 Ω cm.

Some properties of Zn3P2 polycrystalline films prepared by hot‐wall deposition

Zinc phosphide (Zn3P2) thin films have been deposited by hot‐wall deposition technique on glass substrate, and the deposition behaviors as well as structural properties of deposited films are studied. The source temperature and the temperature difference between source and substrate mainly affect the growth rate. Scanning electron microscope observation indicates the growth of columnar structure perpendicular to the substrate, and highly oriented thin films along the c axis are confirmed by x‐ray diffraction analyses. The resistivity of the films is strongly related to the phosphorus composition X in Zn(1−X)PX, and the films having higher X show lower resistivity. The direct absorption edge is obtained as about 1.5 eV from the optical absorption data.

Morphology of GaAs homoepitaxial layer grown on (111) A substrate planes by organometallic vapor phase deposition

Growth behavior of epitaxial layers of GaAs on(111)A plane has been studied for atmospheric pressure organometallic vapor‐phase epitaxy.The arsine partial pressure and the growth temperature are the most influential factors for the surface morphology of the epitaxial layers on (111)A planes. A smooth surface morphology is obtained only under limited growth conditions and a higher AsH3 partial pressure is needed to obtain the mirror surface as the substrate temperature increases. This region is found to spread to higher values of arsine pressure by introducing the predeposition process of thin homoepitaxial layers at the most favorable deposition condition.

Indium doping effects on vapor‐phase growth of ZnS on GaP

Single‐crystal layers of ZnS have been grown on GaP substrates in a hydrogen transport system. By the addition of In to the reactant agents, the orientation dependence of the growth rates of ZnS are reversed for (111)A and (111)B substrates. The improvement of crystallinity of the grown layers can be seen by the surface morphology observation and x‐ray and reflection high‐energy electron diffraction analyses. These phenomena are undoubtedly caused by the In‐incorporation effects during the epitaxial growth of ZnS.

Residual strain and threading dislocation density in InGaAs layers grown on Si substrates by metalorganic vapor-phase epitaxy

InGaAs layers with In contents between 0.007 and 0.055 have been grown on GaAs epilayers on Si substrates by low-pressure metalorganic vapor-phase epitaxy. The threading dislocation density of the order of 105 cm−2 in the InGaAs layer was achieved by insertion of an InGaAs strained layer combined with thermal cycle annealing. Photoluminescence measurement for layers confirmed that the residual strain was lower in InxGa1−xAs layers with x⩾0.038 than that in GaAs. It is suggested that the tensile strain due to the difference in the thermal expansion coefficient between InGaAs and Si materials was compensated by the compressive strain partly due to the slow strain relaxation by work hardening in InGaAs layers grown on GaAs layers or due to the incomplete strain relaxation in InGaAs layers at the small thickness of 1 μm.

The Effects of Iodine-Doping on the Hetero-Epitaxial Growth of ZnS on GaP Substrates

Single-crystalline ZnS layers have been grown on GaP substrates using an open-tube hydrogen transport system. By the addition of iodine to the reactant agents, the growth rate of ZnS on GaP(111)A decreased and that on GaP(111)B increased. These changes of the growth rates caused by the iodine-doping process were characterized as the opposite behavior compared with those for the indium-doping case. For the growth on the GaP(100) plane, the deposition region has largely shifted to lower temperatures, and higher growth rates, such as 5 µm/h, were obtained at considerably lower temperatures, such as 580°C. From an x-ray diffraction analysis, it was found that a significant improvement in the crystallinity of the grown layers on (100) substrates was caused by the doping of iodine. An improvement in the surface morphology for these layers was also clearly observed.

Low temperature growth of InGaAs layers on misoriented GaAs substrates by metalorganic vapor phase epitaxy

InGaAs layers with In composition of 0.57 were grown with metalorganic vapor phase epitaxy (MOVPE) using graded buffer layers on exactly oriented and misoriented GaAs(100) substrates. No mirror-like surface was obtained at growth temperatures between 570 °C and 630 °C. A mirror-like surface was achieved at a growth temperature of 450 °C. The threading dislocation density in the layer grown at 450 °C on the GaAs substrate misoriented toward (111)A was determined to be 1×107 cm−2 using transmission electron microscopy. Photoluminescence results also confirmed that the density of recombination centers in layers grown at 450 °C was low. Low temperature growth with MOVPE was found to be effective in InGaAs layers on GaAs substrates with high In composition above 0.4.