Organometallic chemistry related to applications for microelectronics in Japan

This is meant to be a brief overview of the developments of research activities in Japan on organometallic compounds related to their use in electronic and optoelectronic devices. The importance of organometallic compounds in the deposition of metal and semiconductor films for the fabrication of many electronic and opto-electronic devices cannot be exaggerated. Their scope has now extended to thin-film electronic ceramics and high-temperature oxide superconductors. A variety of organometallic compounds have been used as source materials in many types of processing procedures, such as metal–organic chemical vapor deposition (MOCVD), metalorganic vapor-phase epitaxy (MOVPE), metal–organic molecular-beam epitaxy (MOMBE), etc. Deposited materials include silicon, Group III–V and II–VI compound semiconductors, metals, superconducting oxides and other inorganic materials. Organometallic compounds are utilized as such in many electronic and optoelectronic devices; examples are conducting and semiconducting materials, photovoltaic, photochromic, electrochromic and nonlinear optical materials. This review consists of two parts: (I) research related to the fabrication of semiconductor, metal and inorganic materials; and (II) research related to the direct use of organometallic materials and basic fundamental research.     

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.     

Growth of high-quality GaSb by metalorganic vapor phase epitaxy

The growth of nominally undoped GaSb layers by atmospheric pressure metalorganic vapor phase epitaxy on GaSb and GaAs substrates is studied. Trimethylgallium and trimethylantimony are used as precursors for the growth at 600°C in a horizontal reactor. The effect of carrier gas flow, V/III-ratio, and trimethylgallium partial pressure on surface morphology, electrical properties and photoluminescence is investigated. The optimum values for the growth parameters are established. The carrier gas flow is shown to have a significant effect on the surface morphology. The optimum growth rate is found to be 3–8 μm/ h, which is higher than previously reported. The 2.5 μm thick GaSb layers on GaAs are p-type, having at optimized growth conditions room-temperature hole mobility and hole concentration of 800 cm² V⁻¹ s⁻¹ and 3·10¹⁶ cm^-3, respectively. The homoepitaxial GaSb layer grown with the same parameters has mirror-like surface and the photoluminescence spectrum is dominated by strong excitonic lines.     

Formation of GaAsP interface layers monitored by reflectance anisotropy spectroscopy

Reflectance anisotropy spectroscopy (RAS) has been used to study As-by-P exchange during metalorganic vapor phase epitaxy. The study focuses on the processes occurring during switching from GaAs to GaInP, especially the effect of purging PH₃ over a GaAs surface. GaAsP/GaAs superlattices of different periodicity were grown and the P-content was determined by high-resolution x-ray diffraction and correlated to the RAS spectra. From the temperature dependence of the P-content, an activation energy of 0.56 eV was estimated for the incorporation mechanism. In addition to the insights into the processes at mixed group-V heterointerfaces, our study demonstrates the reproducibility of RAS transients that thus can be used for process monitoring.     

Growth condition of iodine-doped n+-CdTe layers in metal-organic vapor phase epitaxy

Iodine doping of CdTe layers grown on (100) GaAs by metal-organic vapor phase epitaxy (MOVPE) was studied using diethyltelluride (DETe) and diisopropyltelluride (DiPTe) as tellurium precursors and ethyliodine (EI) as a dopant. Electron densities of doped layers increased gradually with decreasing the growth temperature from 425°C to 325°C. Doped layers grown with DETe had higher electron densities than those grown with DiPTe. When the hot-wall temperature was increased from 200°C to 250°C at the growth temperature of 325°C, doped layers grown with DETe showed an increase of the electron density from 3.7×10¹⁶ cm⁻³ to 2.6×10¹⁸ cm⁻³. On the other hand, such an increase of the electron density was not observed for layers grown with DiPTe. The mechanisms for different doping properties for DETe and DiPTe were studied on the basis of the growth characteristics for these precursors. Higher thermal stability of DETe than that of DiPTe was considered to cause the difference of doping properties. With increasing the hot-wall temperature from 200°C to 250°C, the effective ratio of Cd to Te species on the growth surface became larger for layers grown with DETe than those grown with DiPTe. This was considered to decrease the compensation of doped iodine and to increase the electron density of layers grown with DETe. The effective ratio of Cd to Te species on the growth surface also increased with decreasing growth temperature. This was considered to increase the electron density with decreasing growth temperature.     

Atmospheric and low pressure shadow masked MOVPE growth of InGaAs(P)/InP and (In)GaAs/(Al)GaAs heterostructures and quantum wells

The shadow masked growth technique is presented as a tool to achieve thickness and bandgap variations laterally over the substrate during metalorganic vapor phase epitaxy. Lateral thickness and bandgap variations are very important for the fabrication of photonic integrated circuits, where several passive and active optical components need to be integrated on the same substrate. Several aspects of the shadow masked growth are characterized for InP based materials as well as for GaAs based materials. Thickness reductions are studied as a function of the mask dimensions, the reactor pressure, the orientation of the masked channels and the undercutting of the mask. The thickness reduction is strongly influenced by the mask dimensions and the reactor pressure, while the influence of the orientation of the channels and the amount of undercutting is only significant for narrow mask windows. During shadow masked growth, there are not only thickness variations but also compositional variations. Therefore, we studied the changes in In/Ga and As/P ratios for InGaAs and InGaAsP layers. It appears that mainly the In/Ga-ratio is responsible for compositional changes and that the As/P-ratio remains unchanged during shadow masked growth.     

New mechanisms in photo-assisted MOVPE of II-VI semiconductors

The first detailed comparison has been made of the metalorganic vapor phase epitaxy growth rates of CdTe, ZnTe, and ZnSe, measured in situ with laser reflectometry. The comparison also includes the photo-assisted growth with visible radiation from an argon ion laser. Using a standard Group II precursor (DMCd or DMZn.TEN) partial pressure of 1.5 × 10⁻⁴ atm, VI/II ratio of 1 and DIPM (M = Te, Se) the maximum growth rates are in the region of 10 to 15 AU/ s. Decrease in growth rates of ZnTe at higher temperatures or higher laser powers have been attributed to the desorption from the substrate of unreacted Te precursor. The behavior of DTBSe is quite different from DIPSe for both pyrolytic and photo-assisted growth. The maximum growth rate is around 1 AU/ s with very little photo-enhancement, except at 300°C. Secondary ion mass spectroscopy analysis of hydrogen concentration in the ZnSe layers shows high concentrations, up to 5.9 × 10¹⁹ atoms cm⁻³ for DTBSe grown ZnSe under pyrolytic conditions. These results show that the growth kinetics play an important part in the incorporation of hydrogen and passivation of acceptor doped material.     

GaN/GaAs(001)与GaN/Al2O3(0001)外延层光辅助湿法腐蚀行为的比较

研究了用金属有机物气相外延(MOVPE)方法在GaAs(001)衬底上生长的立方相GaN(c-GaN)外延层的光辅助湿法腐蚀特性,并和生长在蓝宝石(0001)衬底上的六方相GaN(h-GaN) 外延层的光辅助湿法腐蚀特性进行了比较.实验发现c-GaN膜的暗态电流和光电流的变化不同于h-GaN膜的腐蚀电流的变化规律.对引起上述差异的原因进行了简单的讨论.     

Impact of growth rate on the quality of ZNS-MQW InGaAsP/InP laser structures grown by LP-MOVPE

We investigated the influence of the growth rate on the quality of zero-net-strained InGaAsP/InGaAsP/InP multiquantum well structures for 1.55 μm emission grown by low pressure metalorganic vapor phase epitaxy. The samples consisted of fixed compressive strained wells (ɛ=+1%) and tensile strained barriers (ɛ=−0.5%) grown with different quaternary bandgap wavelengths (λ_B=1.1–1.4 μm). Using higher growth rates, we obtained for the first time high quality zero net strained multi quantum well structures, regardless having constant group V composition in the well and barriers. The samples were analyzed by x-ray diffraction, photoluminescence and atomic force microscopy techniques. The amplitude of surface modulation roughness along [011] direction decreased from 20 nm to 0.53 nm with increasing growth rate and/or quaternary compositions grown outside the miscibility gap. A new deep PL broad emission band strongly correlated with the onset of wavy layer growth is also reported. Broad area and ridge waveguide lasers with 10 wells exhibited low losses (34 cm⁻¹) and low threshold current densities at infinite cavity length (1020 A·cm⁻² and 1190 A·cm⁻², respectively).     

Criteria for versatile GaN MOVPE tool:high growth rate GaN by atmospheric pressure growth

Growth rate has a direct impact on the productivity of nitride LED production.Atmospheric pressure growth of GaN with a growth rate as high as 10μm/h and also Al_0.1Ga_0.9N growth of 1μm/h by using 4 inch by 11 production scale MOVPE are described.XRD of（002） and（102） direction was 200 arcsec and 250 arcsec, respectively.Impact of the growth rate on productivity is discussed.