Surface Morphology Of Epitaxial Layers Research Articles

Optical and electrical performance of rear side epitaxial emitters for bifacial silicon solar cell application

In this work we investigated the optical and electrical performance of p-type epitaxial layers as the rear emitter of bifacial n-type PERT solar cells. In the first part of this paper, the surface morphology of epitaxial layers grown on textured surfaces is studied. Because of the epitaxial growth, a pyramids-rounding effect is observed as a result of {311} and {911} facet propagation. The growth pattern was quantified and modelled. In the second part of this paper, the optical performance of semi-device test structures is evaluated. The trend of the optical results in bifacial solar cell structures indicates that a final pyramid angle at the rear side around 20° gives the maximum light absorption in the wafer substrate. In this work we demonstrate that the epitaxial growth of the emitter on the textured rear side of these devices can already give a pyramid angle of 25° without having to introduce any additional polishing steps to modify the morphology of the textured surface. In the last part of this paper, we present the electrical results for semi-device structures created to quantify the recombination losses in the passivated and metallized regions of those p-type epitaxial emitters. These results indicate that by introducing a rear epitaxial emitter in the bifacial n-type PERT cell structure, we can increase the implied Voc up to 17 mV compared to a diffused emitter with the same sheet resistance.

Properties of optical and photovoltaic cells on the base of In4Se3, In4(Se3)1-х(Te3)х crystals

Theoretical calculations of thin-film interference systems for design of IR-filters on the base of In4(Se3)1-xTe3x solid solution crystals are carried out. Interference-absorptive band-pass filters on In4(Se3)1-xTe3x crystal with different cutting wavelength position depending on the composition x of the solid solution are produced by vacuum evaporation. Spectral transmission characteristics of the filters and dependence of their parameters on structural perfection of substrates and filter films are studied. Photosensitive elements on the base of In4(Se3)1-xTe3x homo-epitaxial heterojunctions are designed and laser correction of their photosensitivity spectral characteristics is carried out. Surface morphology of epitaxial layers is studied by electron raster microscopy. Temperature dependence of In4(Se3)1-xTe3x based photosensitive elements is measured. Mechanical strength and stability of filters and photosensitive elements spectral characteristics under cooling are studied. Laser treatment of photosensitive elements significantly increases photo-response signal of epitaxial structures at optimal operating temperatures.

4H-SiC ホモエピタキシャル成長における表面モフォロジーのオフ角依存性

We investigated homoepitaxial growth on 4H-SiC substrates with a vicinal off-angle lower than 1°. The small off angle difference of a tenth part of a degree has an influence on surface morphology of epitaxial layers. This tendency also depends on the face polarity and a C-face can be obtained that has a specular surface with a lower vicinal off angle than a Si-face. Low C/Si ratio conditions are also important to control the surface morphology of these substrates. Especially, controlling C/Si ratio with SiH4 flow rate is effective to suppress the generation of step bunching on Si-face epitaxial layers. These results indicate the control of surface free energy is also important to controlling the surface morphology of homoepitaxial growth on these substrates.

Epitaxial Growth of n-Type 4H-SiC on 3" Wafers for Power Devices

In this paper we present recent results of epitaxial growth of 4H-SiC on 3” (0001) 8° and 4° off-oriented wafers using a multi-wafer hot-wall CVD system. This equipment exhibits a capacity of 5x3” or 7x2” wafers per run. By optimizing the process conditions epitaxial layers with excellent crystal quality, purity and homogeneity in doping and thickness were grown. The intra-wafer as well as the wafer-to-wafer homogeneity will be illustrated by doping and thickness mappings of a full-loaded run. Surface morphology of epitaxial layers on 8° and 4° off-oriented wafers was investigated by atomic force microscopy.

Low temperature epitaxial growth of InP by remote plasma-assisted metalorganic chemical vapor deposition

Epitaxial growth of InP at 400°C or below has been carried out by using remote plasma-assisted metalorganic chemical vapor deposition (RPMOCVD). Source materials of trimethylindium (TMI) and phosphine (PH 3) are decomposed by remote hydrogen plasma. The increased RF power for exciting remote plasma improves the surface morphology of epitaxial layers. Epitaxial growth of InP layers with smooth mirror surface is achieved at a temperature as low as 275°C, an RF power of 75 W and a gas pressure of 3 Torr. The growth temperature is much lower than the thermal decomposition temperature of TMI and PH 3. No strong dependence of the growth rate on the substrate temperature is demonstrated.

Morphology of AlGaAs layer grown on GaAs(111)A substrate plane by organometallic vapor phase epitaxy

Growth behavior of AlGaAs heteroepitaxial layers on GaAs (111)A planes has been studied for atmospheric pressure organometallic vapor phase epitaxy. The Al composition as well as the arsine partial pressure and the growth temperature are the influential factors for the surface morphology of epitaxial layers on (111)A planes. By increasing the Al composition of grown layers, the range of growth conditions for obtaining a smooth surface morphology does not change so much. But the range for controlling defect structures, such as pyramidal shape, shifts to lower arsine partial pressures, and/or higher growth temperatures. The Al0.3Ga0.7As growth rate remains constant even at a lower arsine partial pressure than for the GaAs growth. This indicates that the morphology change is due to the increase in the arsine dissociation efficiency when the trimethylaluminum partial pressure increases.

Chemical vapor transport in the ZnTe-HCl closed-tube system and its thermodynamic analysis

The chemical vapor transport and homoepitaxial growth of ZnTe are investigated in the ZnTe-HCl closed-tube system. The transport rate increases monotonically until 0.1 mg/cm 3 and then increases rapidly with the increase of HCl concentration. The growth rate of the (110) epi-layer has the same HCl concentration dependence as the transport rate. The surface morphology of epitaxial layers grown on (110) substrate is uneven, while that on (110) substrate is relatively smooth. Large amounts of dendritic crystals are observed deposited on the ampoule at high HCl concentration where the high transport rate occurs. The experimentally obtained transport rate can be explained quantitatively over the whole range of HCl concentration using thermodynamic calculations considering laminar, diffusion and convection flows.

Epitaxial growth and chemical vapor transport of ZnTe by closed-tube method

The epitaxial growth of ZnTe in a ZnTe- I 2 system by a closed tube method is investigated by varying the charged iodine concentration ( M I 2) or the temperature difference ( ΔT) between the high and low temperature zones. The transport rate is a function of M I 2 and ΔT and has a minimum value increasing monotonically at higher and lower iodine concentration, and it increases with increasing ΔT. This experimental result can be explained well by thermodynamical calculations. The growth rate of ZnTe has the same tendency as the transport rate. The surface morphology of epitaxial layer on (110)ZnTe is not sinificantly affected by M I 2 but becomes smoother with increasing temperature. The surface morphology and the growth rate of ZnTe layers also depend upon the orientation of substrate. The epitaxial layer can be obtained at temperature as low as 623°C.