Compositional non-uniformities in selective area growth of GaInAs on InP grown by OMVPE

Selective area epitaxial growth of Ga_0.47In_0.53As on InP substrates patterned with silicon nitride was done by low pressure organometallic vapor phase epitaxy. Good surface morphology and clean side walls of the epitaxial layers were obtained in most of the areas of selective GalnAs growth. However, both GaAs incorporation and InAs incorporation increased near the edges of the selective growth areas due to the extra flux of Gacontaining and In-containing species migrating on the surface of silicon nitride. The increase in InAs incorporation was found at a higher rate when the adjacent silicon nitride area was large, hence, cross-hatching appeared near the edges. A characteristic length of adjacent silicon nitride seemed to be connected with the enhanced InAs incorporation, which was about 40μm at 600°. The non-uniformities in composition appeared in all wafers grown in the temperature range between 570 and 650°.     

Tin-doping ofn + InP OMVPE layers

Tin as a donor dopant in OMVPE epilayers of InP has been studied for its dependence on growth parameters to assess the nature of the dopant incorporation from a tetraethyltin (TESn) source and to establish reproducible conditions for tailoring carrier concentrations. Free carrier concentrations depend linearly on Sn/In ratio and are independent of PH₃ concentration consistent with the impurity incorporation on In-lattice sites. The carrier concentration saturates at 3 × 10¹⁹ cm³ and is accompanied by excess Sn accumulation on the layer surface. X-ray diffraction shows an expansion of the lattice proportional both to the measured free carrier concentration and to the TESn gas concentration up to solid saturation. The lattice expansion is larger than expected from Sn for In radius substitution. SIMS profiles for abrupt turn-on and turn-off of the dopant source show transient changes of Sn concentration consistent with a Sn surface layer buildup.     

Tellurium induced lattice dilation in OMVPE grown InP

For organometallic vapor phase epitaxial (OMVPE) grown InP, the change in lattice constant is measured as a function of tellurium (Te) dopant concentration. We observe ~0.15% dilation in the InP lattice constant at a Te concentration of ~10²⁰ cm^-3. Our measurements are compared to predictions from Vegard’s Law.     

The inverted horizontal reactor: Growth of uniform InP and GaInAs by LPMOCVD

The uniformity of InP and GalnAs lattice matched to InP has been studied for three different types of horizontal reactors. Employing the conventional approach,i.e. the susceptor is positioned in the centre or at the bottom of the reactor cell with the wafer surface facing upward, the uniformity in film thickness and ternary composition perpendicular to the direction of gas flow could be substantially improved by using an obstacle which spreads the incoming gas over the entire width of the reactor. In the direction of flow however, a compositional grading of the GalnAs films was observed. This gradient could be avoided by using a novel design in which the substrate is located at the highest and hottest point of the reaction cell and facing downwards.     

Characterization of InP grown by OMVPE using trimethylindium and tertiarybutylphosphine (TBP) at low V/III ratios and reduced TBP partial pressures

We report an OMVPE growth process for InP using trimethylindium (TMI) and tertiarybutylphosphine (TBP), a V/III ratio of 15, and a TBP partial pressure of 0.5 Torr. Growth is initiated with a 0.1 μm buffer layer employing a ramped TBP flow. Results are presented for InP grown with two different samples of both TMI and TBP and compared to previous experimental results and theoretical predictions. Good surface morphology is obtained from 540 to 600° C. The net carrier concentrations, N_d-N_a, decrease with increasing growth temperature—but never fall below 1.3 × 10¹⁶ cm^-3. Mobilities of 3990 and 11200 cm²/V.sec are observed at 300 and 77 K, respectively. At 77 K, we infer a compensation ratio of ∼0.4, independent of N_d-N_a. Photoluminescence measurements at 6 K show intense near bandgap emission with a full width half maximum proportional to N_d-N_a. Weak emission is also observed from carbon acceptors, independent of growth temperature. Secondary ion mass spectroscopy measurements are performed on an InP wafer grown with four different temperatures. The observed sulfur concentration drops from 1 × 10¹⁸ to 6 × 10¹⁶ cm^-3 with increasing growth temperature. This confirms that sulfur is an important residual impurity in TBP. The observed carbon concentration is 4–6 × 10¹⁶ cm^-3, regardless of growth temperature.     

Non-hydride group V sources for OMVPE

A major limitation to the continuing development of organometallic vapor phase epitaxy (OMVPE) for the growth of III/V semiconductor materials is the hazard posed by the hydride sources, AsH₃ and PH₃, which are virtually universally used, in high pressure cylinders, as the group V source materials for the growth of the highest quality materials. The ideal group V source would be a nontoxic liquid with a moderate vapor pressure (50-500 Torr). To be suitable for OMVPE growth, the molecule must pyrolyze at ordinary growth temperatures, be stable against decomposition in the bottle at room temperature, and not participate in undesirable parasitic reactions with the group III source molecules. The new sources have additional constraints related to purity. They must be easily purified without decomposing and produce no detectable carbon contamination in the resultant epitaxial layers. This set of stringent requirements eliminates most commonly available non-hydride group V sources. Recent research on newly developed sources has shown considerable promise. The entire area of group V sources, including the elemental sources, for OMVPE growth of III/V materials will be reviewed. The sources with no hydrogen atoms attached to the group V atom, the elemental, trimethyl-V, and triethyl-V, sources all appear to give unacceptably high carbon incorporation. Diethylarsine, which has one H attached to the As, produces high quality GaAs but has an inconveniently low vapor pressure. Trimethylphosphine and triethylphosphine o not pyrolyze at low enough temperatures to be useful for conventional OMVPE growth. Tertbutylarsine (TBAs) and tertbutylphosphine (TBP) appear to be promising source materials. TBP has a very low toxicity, a vapor pressure ideal for OMVPE growth, and the pyrolysis occurs at lower temperatures than for PH₃, allowing the use of low values of V/III ratio for the growth of high quality material. No carbon contamination can be attributed to the TBP. Control of the As/P ratio in OMVPE grown GaAsP is much improved for TBP as compared with PH₃ due to the more rapid pyrolysis. At normal growth temperatures the P distribution coefficient is nearly unity. TBAs has been less studied, but appears to have similar attributes including a favorable vapor pressure and lower pyrolysis temperature than AsH₃, allowing OMVPE growth of GaAs at low values of V/III ratio. The substitution of TBAs for AsH₃ results in no observable increase in carbon in the epitaxial GaAs.     

OMVPE growth of InP and Ga0.47ln0.53as using ethyldimethylindium

We report the organometallic vapor phase epitaxial (OMVPE) growth of InP and Ga_0.47In_0.53As using a new organometallic indium source, ethyldimethylindium (EDMIn), rather than the traditional sources triethylindium (TEIn) or trimethylindium (TMIn). EDMIn is a liquid at room temperature and its vapor pressure at 17° C was found to be 0.85 Torr using thermal decomposition experiments. The growth results using EDMIn were compared to those using TMIn in the same atmospheric pressure reactor. For InP, use of EDMIn resulted in a high growth efficiency of 1.3 × 10⁴ μm/ mole, which was independent of the growth temperature and comparable to the growth efficiency obtained with TMIn. The high growth efficiency is consistent with the observation of no visible parasitic gas phase reactions upstream of the substrate. The 4K photoluminescence (PL) spectra consist of a peak due to bound excitons and an impurity related peak 38 meV lower in energy. This impurity peak is ascribed to conduction band to acceptor transitions from carbon, due to the decreasing relative intensity of this peak with increasing V/III ratio. The relative intensity of the C impurity peak decreases by five times when the growth temperature is increased from 575 to 675° C, with a corresponding increase in the room temperature electron mobility from 725 to 3875 cm²/ Vs. For GalnAs lattice-matched to InP, use of EDMIn also resulted in a temperatureindependent high growth efficiency of 1.0 x 10⁴ μm/mole, indicating negligible parasitic reactions with AsH₃. The In distribution coefficient was nearly constant at a value of 0.9, however the run to run composition variation was slightly higher for EDMIn than for TMIn. The 4K PL showed donor-acceptor pair transitions due to C and Zn. The C impurity peak intensity decreased dramatically with increasing growth temperature, accompanied by an increase in the room temperature electron mobility to 5200 cm²/Vs. Overall, the growth of both InP and GalnAs using EDMIn was qualitatively similar to that using TMIn, although the room temperature electron mobilities were lower for the new source than for our highest purity bottle of TMIn.     

Selective growth of InP on patterned,nonplanar InP substrates by low-pressure organometallic vapor phase epitaxy

The effects of indium sources, mask materials and etched mesa profiles on growth mor-phology of Fe-doped semi-insulating InP on patterned, nonplanar InP substrates were studied for low-pressure organometallic vapor phase epitaxy (OMVPE). The presence or absence of polycrystalline InP layers deposited on the mask was found to depend on the indium source but not on the mask material. Trimethylindium was found to be the preferable indium source for prevention of polycrystalline InP deposits on the mask. The etched mesa shape was found to dominate the final geometry of the OMVPE re-grown InP layer. Inclusion of an interfacial layer of 1.16 μm bandgap wavelength InGaAsP between the dielectric mask and InP substrate produces a favorable mesa shape by con-trolling the level of undercut during mesa etching, so as to form a smooth mesa profile. After selective regrowth of InP over the resulting mesa, a planar surface is typically achieved for mesa stripes with a mask overhang length as long as 2.6 μm and a mesa height as high as 4 μm.     

Growth of AIGalnP in a high-speed rotating disk OMVPE reactor

In an OMVPE reactor with a high speed rotating disk, growth of a quaternary material AIGalnP is carried out after a basic investigation on the GaAs growth rate uniformity. Experimental growth rate and growth efficiency results are compared with the theoretical results obtained from an infinite diameter rotating disk model. Distributions of the lattice mismatch, PL spectra and carrier concentration were measured to clarify the disk rotation effect on these properties. The main reason for non-uniformities is not the disk rotation but the temperature distribution on a substrate carrier.     

Design and process development of a novel multi-wafer OMVPE reactor for growing very uniform GaAs and AlGaAs epitaxial layers

A unique multi-wafer OMVPE reactor with capability to produce atomic-layer abrupt-ness is demonstrated. Uniform GaAs and AlGaAs epitaxial layers were grown on four two-inch wafers or one three- or four-inch wafer. Thickness variation across a three-inch wafer was less than ±2%, while the variation of Al solid composition was less than ±1%. Multiple AlGaAs/GaAs quantum wells ranging in size from 10Å to 140Å were grown with heterointerface roughness less than one monolayer. The electrical properties of HEMT device were studied. Variations of sheet carrier concentration and electron mobility were ±6% and ±5% respectively across a three-inch wafer. The carrier con-centration profile, mobility spectrum and device characteristics of DH-HEMT are also presented. These results indicate that this OMVPE reactor can grow good device struc-tures for microwave and millimeter-wave power device applications.     

AFM observation of OMVPE grown ErP on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates

ErP has been grown on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates by low-pressure organometallic vapor-phase epitaxy. The morphological change with growth temperature has been explored by atomic force microscope. On all the substrates, ErP is grown in island structure. Height and area size of the ErP islands on (1 1 1)A substrate exhibit an obvious dependence on growth temperature. ErP islands grown at 540°C, that is the suitable temperature for ErP formation, gather to step edges to make wires.     

一种制备大面积超导薄膜的激光扫描淀积方法

本文报道了一种制备大面积超导薄膜的激光扫描淀积方法。这种方法是通过一光学变换传输系统使激光束能绕一定的半径旋转,旋转的激光束去扫描消融超导靶材来淀积大面积超导薄膜。实验表明用这种激光扫描淀积方法可使超导薄膜的均匀区域扩大10倍左右。     

激光扫描制备大尺寸超导薄膜的理论分析

提出了利用激光扫描剥离靶材,沉积膜厚分布均匀的大尺寸高温超导薄膜分析模型。利用这模型取得的结果表明:激光扫描方法沉积的薄膜厚度分布依赖于激光扫描半径、靶面与基片的间距。对于一定均匀性程度要求的薄膜,存在一个能获得最大尺寸薄膜的最佳激光扫描半径。实验结果与理论分析基本一致。     

Pyrolysis of 1,1 dimethylhydrazine for OMVPE growth

A key requirement for the growth of the wide bandgap nitrides, GaN and InGaN, is providing a sufficient supply of atomic nitrogen from the vapor phase during growth. In order to prevent a high concentration of nitrogen vacancies, especially for GaInN, one strategy is to use a precursor with a low pyrolysis temperature, thus yielding a high concentration of atomic nitrogen in the vapor phase. 1,1 dimethylhydrazine (DMHy), with an appropriate vapor pressure of 157 Torr at 25°C and a low pyrolysis temperature (T₅₀∼420°C), is a promising candidate to replace NH₃, the most common nitrogen source. The pyrolysis studies of DMHy suggest the rate limiting step for decomposition is a heterogeneous, unimolecular process that is independent of both input concentration and ambient. Radical reactions are also involved as indicated by the products. In He they include CH₄, NH₃, N₂, H₂, HCN, C₂H₆, CH₃NCH₂, and (CH₃)₂NH. Experiments on the copyrolysis of DMHy and trimethylgallium show that an adduct is formed at room temperature followed by CH₄ elimination, presumably forming (CH₃)₂GaNHN(CH₃)₂. At higher temperatures, the products indicate that the covalent Ga-N bond doesn’t dissociate during pyrolysis.     

Effects of pressure and temperature on epitaxial growth of InP on non-planar substrates using OMVPE

The effects of pressure and temperature on the epitaxial growth of InP on the mesastructured substrate have been investigated using OMVPE. At 550° C and 700 Torr, the reverse-mesa profile was observed. As the pressure decreases, the epitaxial growth profile changes from the reverse-mesa shape to the mesa shape. As the growth temperature increases, the growth profile follows the mesa-structured substrate even at high growth pressure. We propose that two major factors contributed to the formation of the reverse-mesa shape at low temperature and high pressure. We can explain the pressure effects on the epitaxial growth profile with these two factors at all growth temperatures ranging from 550 to 650° C. One factor is the growth rate enhancement on the (111)A facet compared to the growth rate on the (001) facet at low growth temperature, the other is the deficiency of constituent at the recess region of the epitaxial layer caused by reduced gas phase diffusivity at high pressure.     

Large-area uniform OMVPE growth for GaAs/AIGaAs quantum-well diode lasers with controlled emission wavelength

The properties of GaAs and AlGaAs epilayers grown in a vertical rotating-disk OMVPE reactor operated at reduced pressure (0.2 atm) are extremely uniform. For substrate rotation at 500 rpm, the thickness uniformity is ±1% for thick epilayers and ±2% for quantum wells 3−10 nm thick. The coefficient of variation in aluminum composition is 1.8 × 10⁻³ or less. For broad-area GRIN-SCH diode lasers containing a single-quantumwell active layer, the threshold current density and differential quantum efficiency are highly uniform. The laser emission wavelength is precisely controlled by adjusting the active layer thickness and composition. For 175 devices distributed over a 16-cm² wafer containing a 10-nm-thick Al_0.07Ga_0.93As active layer, the total variation in emission wavelength is 3.0 nm. For all of these devices and for test devices from nine additional wafers, the wavelengths range from 803.5 to 807.4 nm.     

Ultra-low temperature OMVPE of InAs and InAsBi

InAs and InAsBi have been grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE) over a broad temperature range from 600 to as low as 275° C. This is the lowest growth temperature ever reported for conventional OMVPE. It is demonstrated that lowering the growth temperature is the most effective approach for increasing the maximum Bi content in InAsBi alloys where the Bi solubility limit is 0.025 at.%. For example, InAsBi samples with Bi concentrations as high as 6.1 at.% have been successfully grown at a temperature of 275° C. Trimethylindium, arsine, and trimethylbismuth were used as precursors for most experiments. The growth efficiency is a constant for temperatures above 400° C, indicating that the growth rate is diffusion limited. For lower temperatures, it decreases exponentially with decreasing temperature with an activation energy of 24 kcal/mol. Incomplete pyrolysis of TMIn limits the growth rate in this temperature regime. By substituting ethyldimethylindium for TMIn the growth rate can be increased at lower temperatures. Hall effect measurements show that then-type background concentration increases from approximately 2.3 × 10¹⁶ to 10¹⁹ cm⁻³ as the growth temperature decreases from 600 to 325° C. Secondary ion mass spectroscopy results show that the dominant impurity is carbon. Thus, carbon is mainly a donor in these materials. The integrated photoluminescence intensity drops rapidly with decreasing growth temperature.     

一种包含热效应的InP DHBT大信号模型及其Verilog-A实现

A large signal model for InP/InGaAs double heterojunction bipolar transistors including thermal effects has been reported,which demonstrated good agreements of simulations with measurements.On the basis of the previous model in which the double heterojunction effect,current blocking effect and high current effect in current expression are considered,the effect of bandgap narrowing with temperature has been considered in transport current while a formula for model parameters as a function of temperature has been developed.This model is implemented by Verilog-A and embedded in ADS.The proposed model is verified with DC and large signal measurements.     

OMVPE growth of In0.53Ga0.47As on InP using tertiarybutylarsine

We have successfully grown bulk In_0.53Ga_0.47As on InP using tertiarybutylarsine (TBA), trimethylindium and trimethylgallium. The growth temperature was 602° and the V/III ratio ranged from 19 to 38. Net carrier concentrations were 2 – 4 × 10¹⁵ cm^-3, n-type, with a peak 77 K mobility of 68,000 cm²/V. sec. Increasing compensation was observed in In_0.53Ga_0.47As grown at higher V/III ratios. PL spectra taken at 5 K revealed strong near bandgap emission at 0.81 eV—with the best sample having a FWHM of 2.5 meV. At lower energies, donor-acceptor pair transitions were evident. Strong and sharp 5 K PL emission was observed from InP/In_0.53Ga_0.47As/InP quantum wells grown with TBA.     

In-situ OMVPE process sensing of GaAs and AlGaAs by photoreflectance

The contactless electromodulation method of photoreflectance has been successfully applied as an in-situ sensor of the OMVPE process. The direct band gap,E ₀, of GaAs and AIGaAs has been measured, in-situ, under OMVPE growth conditions. To the best of our knowledge, this is the first report of an in-situ photoreflectance measurement of III-V materials properties in an OMVPE system. This is significant in that it illustrates the potential for the application of photoreflectance as an in-situ process monitor, analogous to the use of RHEED measurements in MBE. The GaAs substrate temperature of 650°, as measured by an optical pyrometer, corresponds to the temperature derived using the Varshni equation and published Varshni coefficients to within the error of the published data.