Characterization of n-type Ge layers on Si (100) substrates grown by rapid thermal chemical vapor deposition

Phosphorus-doped n-type Ge layers were grown on p-type Si (100) wafers (8 in. in diameter, resistivity 5–15 Ω cm) using rapid thermal chemical vapor deposition (RTCVD). The surface morphology was very smooth, with a root mean square (RMS) surface roughness of 0.29 nm. The in-plane lattice constant calculated from high-resolution X-ray diffraction (HR-XRD) data was 0.5664 nm, corresponding to in-plane tensile strain of ～0.47%. The Raman Ge peak for each location indicates tensile strain from the Ge wafer. We estimated the in-plane strain as tensile strain of ～0.45%, in excellent agreement with the XRD analysis. Initial photocurrent spectrum experiments on the sample confirm valence band splitting of the direct gap induced by tensile strain. The temperature dependence of the direct bandgap energy E_Γ1 of Ge can be described by the empirical Varshni expression E_Γ1(T)=0.864–5.49×10^–4T ²/(T+296).     

Mechanism of hemispherical-grained Si formation for dynamic random access memory cells by rapid thermal chemical vapor deposition

An uneven coating made of hemispherical-grained Si (HSG) was formed on an amorphous Si layer by a rapid thermal chemical vapor deposition (CVD) (RTCVD) process. The uneven coating increases the effective surface area of a capacitor electrode in dynamic random access memory (DRAM) cells. The formation of the HSG consists of “seeding” and subsequent isothermal annealing stages. During the seeding stage, nanometer size Si single crystals are formed on the surface of the amorphous Si layer. During rapid thermal annealing at 665°C, under high vacuum, the Si grains grow linearly with increasing temperature and reach an average size of 95 nm after 20 sec. The nucleation and growth of the HSG occurs within a narrow range of temperature and time, which is sufficient for a short diffusion path of Si atoms on the surface of the amorphous Si layer, but insufficient for crystallization of the amorphous Si layer: The HSG coating increases the capacitance of a memory cell by a factor of 2.     

Growth and characterization of GaAs films deposited on Ge/Si composite substrates by metalorganic chemical vapor deposition

We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied, the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates.     

Ge/Si(100)界面互扩散的喇曼光谱

利用喇曼光谱研究了不同温度下在Si(100)衬底上异质外延Ge层由于扩散引起的Ge/Si异质结界面互混以及表面活化剂Sb对其的影响.结果表明表面活化剂Sb的存在大大抑制了界面的互扩散,在650℃下也没有观察到明显的界面互混.没有Sb时,在500℃下已存在一定程度的界面互混,界面互混程度随外延层生长温度的增高而增强.这种互扩散的差别与成岛生长时应变释放有关     

Initial stages of GaN/GaAs (100) growth by metalorganic chemical vapor deposition

We have investigated the growth of GaN buffers by metalorganic chemical vapor deposition (MOCVD) on GaAs (100) substrates. Atomic force microscope (AFM) and reflection high-energy electron diffraction (RHEED) were employed to study the dependence of the nucleation on the growth temperature, growth rate, annealing effect, and growth time. A two-step growth sequence must be used to optimize and control the nucleation and the subsequent growth independently. The size and distribution of islands and the thickness of buffer layers have a crucial role on the quality of GaN layers. Based on the experimental results, a model was given to interpret the formation of hexagonal-phase GaN in the cubic-phase GaN layers. Using an optimum buffer layer, the strong near-band emission of cubic GaN with full-width at half maximum (FWHM) value as small as 5.6 nm was observed at room temperature. The background carrier concentration was estimated to be in the range of 10¹³ ∼ 10¹⁴ cm⁻³.     

Effects of oxygen doping on properties of microcrystalline silicon film grown using rapid thermal chemical vapor deposition

An oxygen doped microcrystalline silicon (μc-Si) deposition process is developed by mixing small amounts of nitrous oxide (N₂O) with silane (SiH₄) in a rapid thermal chemical vapor deposition (RTCVD) reactor. The effects of oxygen doping on the properties of RTCVD μc-Si films are studied. Experimental results show that the RTCVD process provides high deposition rates for μc-Si and polycrystalline silicon (polySi) films at elevated deposition temperatures and pressures. The surface roughness of the RTCVD μc-Si films can be significantly reduced compared to that of conventional LPCVD polySi films. Steep side walls can be realized due to the small grain size of the μc-Si films. The sheet resistance of BF₂ doped μc-Si films is slightly higher than that of BF₂ doped polySi films, whereas sheet resistances of P and As doped μc-Si films are much higher than those of the corresponding P and As doped polySi films. Measurements of the catastrophic breakdown strength of metal-oxide-semiconductor (MOS) capacitors indicate that the quality of gate electrodes fabricated using μc-Si is improved relative to that of MOS capacitors fabricated using polySi gate electrodes.     

Interaction of self-assembled Ge islands and adjacent Si layers grown on unpatterned and patterned Si(001) substrates

For use in electronic devices, self-assembled Ge islands formed on Si(001) must be covered with an additional Si layer. Chemically vapor deposited Si layers initially grow very rapidly over Ge islands because of the catalytic effect of Ge on the reaction of the Si-containing gas. The edges of the Si features covering Ge “pyramids” are rotated by 45° with respect to the edges of the Ge pyramids because of the different mechanisms orienting the Ge islands and the Si features. When multiple layers of islands are formed, the in-plane ordering of the Ge islands depends on the thickness of the Si interlayer separating the island layers. When selective Si is grown on a patterned Si wafer to form the underlying structure for the Ge islands, the position of the islands is influenced by the detailed shape of the Si near the edges, which in turn depends on the thickness of the selectively deposited Si, the pattern size, and the amount of surrounding oxide.     

Structural analysis of Ge x Si1−x /Si layers by remote plasma-enhanced chemical vapor deposition on Si (100)

In this work, remote plasma-enhanced chemical vapor deposition (RPCVD) has been used to grow Ge _x Si_1−x /Si layers on Si(100) substrates at 450° C. The RPCVD technique, unlike conventional plasma CVD, uses an Ar (or He) plasma remote from the substrate to indirectly excite the reactant gases (SiH₄ and GeH₄) and drive the chemical deposition reactions. In situ reflection high energy electron diffraction, selected area diffraction, and plan-view and cross-sectional transmission electron microscopy (XTEM) were used to confirm the single crystallinity of these heterostructures, and secondary ion mass spectroscopy was used to verify abrupt transitions in the Ge profile. XTEM shows very uniform layer thicknesses in the quantum well structures, suggesting a Frank/ van der Merwe 2-D growth mechanism. The layers were found to be devoid of extended crystal defects such as misfit dislocations, dislocation loops, and stacking faults, within the TEM detection limits (∼10⁵ dislocations/cm²). Ge _x Si_1−x /Si epitaxial films with various Ge mole fractions were grown, where the Ge contentx is linearly dependent on the GeH₄ partial pressure in the gas phase for at leastx = 0 − 0.3. The incorporation rate of Ge from the gas phase was observed to be slightly higher than that of Si (1.3:1).     

Dislocation profiles in HgCdTe(100) on GaAs(100) grown by metalorganic chemical vapor deposition

We studied dislocation etch pit density (EPD) profiles in HgCdTe(lOO) layers grown on GaAs(lOO) by metalorganic chemical vapor deposition. Dislocation profiles in HgCdTe(lll)B and HgCdTe(lOO) layers differ as follows: Misfit dislocations in HgCdTe(lll)B layers are concentrated near the HgCdTe/CdTe interfaces because of slip planes parallel to the interfaces. Away from the HgCdTe/CdTe interface, the HgCdTe(111)B dislocation density remains almost constant. In HgCdTe(lOO) layers, however, the dislocations propagate monotonically to the surface and the dislocation density decreases gradually as dislocations are incorporated with increasing HgCdTe(lOO) layer thicknesses. The dislocation reduction was small in HgCdTe(lOO) layers more than 10 μm from the HgCdTe/CdTe interface. The CdTe(lOO) buffer thickness and dislocation density were similarly related. Since dislocations glide to accommodate the lattice distortion and this movement increases the probability of dislocation incorporation, incorporation proceeds in limited regions from each interface where the lattice distortion and strain are sufficient. We obtained the minimum EPD in HgCdTe(100) of 1 to 3 x 10⁶ cm^-2 by growing both the epitaxial layers more than 8 μm thick.     

硼原子对Si(100)衬底上Ge量子点生长的影响

研究了硼原子对 Si( 1 0 0 )衬底上 Ge量子点自组织生长的影响 .硼原子的数量由 0单原子层变到 0 .3单原子层 .原子力显微镜的观察表明 ,硼原子不仅对量子点的大小 ,而且对其尺寸均匀性及密度都有很大影响 .当硼原子的数量为 0 .2单原子层时 ,获得了底部直径为 60± 5nm,面密度为 6× 1 0 9cm- 2 ,且均匀性很好的 Ge量子点 .另外 ,还简单讨论了硼原子对 Ge量子点自组织生长影响的机制 .     

High quality gate dielectrics formed by rapid thermal chemical vapor deposition of silane and nitrous oxide

In the present study, we have performed electrical characterization of oxides deposited via rapid thermal chemical vapor deposition using SiH₄ and N₂O. We have investigated the effect of temperature, pressure, and SiH₄ to N₂O ratio on the electrical and material properties of as-deposited films. We have found that as-deposited oxides deposited at low temperatures, low pressures, and with a low silane to nitrous oxide ratio of ～0.5% give good material and electrical properties. The as-deposited films are stoichiometric in nature and have high deposition rates. As-deposited films had very low D_it values, high breakdown fields, and excellent subthreshold swing. The leakage currents and metal oxide semiconductor field effect transistor current drive, although lower than thermal oxides, were found to be quite acceptable. We have also investigated the thickness dependence of the films and found that as the film thickness is reduced below 50Å, the reliability improves for all oxides including the silicon-rich deposited oxides.     

X-ray microdiffraction investigation of crystallinity and strain relaxation in Ge thin lines selectively grown on Si(0 0 1) substrates

We used X-ray microdiffraction (XRMD) to investigate the crystallinity and strain relaxation of Ge thin lines with widths of 100, 200, 500 and 1000 nm selectively grown on Si(0 0 1) substrates using a patterned SiO₂ mask by chemical vapor deposition. The variations of the strain relaxation in the line and width directions were also investigated in Ge thin lines with a width of 100 nm. After growth, crystal domains with very small tilt angles were detected in Ge lines with all four line widths. The tilt angle range was larger in thinner Ge lines. After annealing at 700 °C, the formation of a single, large domain with a specific tilt angle was detected by XRMD for Ge thin lines with widths of 100 and 200 nm. These experimental results reflect the effects of SiO₂ side walls around the Ge thin lines on crystallinity and strain relaxation of Ge.     

Formation of titanium and cobalt germanides on Si (100) using rapid thermal processing

Titanium and cobalt germanides have been formed on Si (100) substrates using rapid thermal processing. Germanium was deposited by rapid thermal chemical vapor deposition prior to metal evaporation. Solid phase reactions were then performed using rapid thermal annealing in either Ar or N₂ ambients. Germanide formation has been found to occur in a manner similar to the formation of corresponding silicides. The sheet resistance was found to be dependent on annealing ambient (Ar or N₂) for titanium germanide formation, but not for cobalt germanide formation. The resistivities of titanium and cobalt germanides were found to be 20 μΩ-cm and 35.3μΩ-cm, corresponding to TiGe₂ and Co₂Ge, respectively. During solid phase reactions of Ti with Ge, we have found that the Ti₆Ge₅ phase forms prior to TiGe₂. The TiGe₂ phase was found to form approximately at 800° C. Cobalt germanide formation was found to occur at relatively low temperatures (425° C); however, the stability of the material is poor at elevated temperatures.     

Effect of gas feeding methods on optical properties of GaN grown by rapid thermal chemical vapor deposition reactor

The origin of the radiative recombination leading to yellow luminescence (YL) has been elucidated by the study of luminescence properties of GaN films grown with two different gas feeding methods. GaN films were grown on a (0001) sapphire substrate in a rapid thermal chemical vapor deposition (RTCVD) reactor. GaN films emitted two different luminescence energies, 2.2 and 3.47 eV, depending on the introducing position of hydrogen gas in the growth reactor. The distribution of the TMGa flow and gas phase reactions in the reactor were investigated to understand the effect of the gas feeding methods on the optical properties of GaN films. The results suggest that YL is related to Ga vacancies in the grown films.     

Strained single-crystal GOI (Ge on Insulator) arrays by rapid-melting growth from Si (1 1 1) micro-seeds

Liquid-phase epitaxial growth of Ge islands on insulator (GOI) using Ni-imprint-induced Si (1 1 1) micro-crystal seeds (∼1 μm?) is proposed. As a result, single-crystalline GOI (1 1 1) structures with large area (∼10 μm?) are realized. The transmission electron microscopy observations reveal no dislocation or stacking fault in the laterally grown regions. Moreover, the Raman measurements show that the tensile strain (∼0.2%) which enhances the carrier mobility is induced in the growth regions. This new method can be employed to realize the multi-functional SiGe large scale integrated circuits.     

Photoluminescence of phosphorous doped Ge on Si (100)

Photoluminescence (PL) of selectively grown phosphorus (P) doped germanium (Ge) is investigated. 350–600 nm thick P-doped Ge is grown on 100 nm thick P-doped Ge buffer layer, which is annealed at 800 °C before the main part of Ge deposition. In the case of Ge deposited at 325 °C, approximately two times higher PL intensity is observed by P doping of ~3.2×10¹⁹ cm⁻³. Further increase of PL intensity by a factor of 1.5 is observed by increasing the growth temperature from 325 °C to 400 °C due to improved crystal quality. Varying PH₃ partial pressure at 400 °C, red shift of the PL occurred with increasing P concentration due to higher bandgap narrowing. With increasing P concentration up to ~1.4×10¹⁹ cm⁻³ at 400 °C the PL peak intensity increases by filling electrons into the L valley and decreases due to enhanced point defect concentration and degraded crystallinity. By post-annealing at 500–800 °C, the PL intensity is further increased by a factor of 2.5 because of increased active P concentration and improved crystal quality. Reduced direct bandgap energy by introducing tensile strain is also observed.     

Structural characterization of thick, high-quality epitaxial Ge on Si substrates grown by low-energy plasma-enhanced chemical vapor deposition

In this paper, we report on the growth of epitaxial Ge on a Si substrate by means of low-energy plasma-enhanced chemical vapor deposition (LEPECVD). A Si_1?xGe_x graded buffer layer is used between the silicon substrate and the epitaxial Ge layer to reduce the threading dislocation density resulting from the lattice mismatch between Si and Ge. An advantage of the LEPECVD technique is the high growth rate achievable (on the order of 40 Å/sec), allowing thick SiGe graded buffer layers to be grown faster than by other epitaxial techniques and thereby increasing throughput in order to make such structures more manufacturable. We have achieved relaxed Ge on a silicon substrate with a threading dislocation density of 1 × 10⁵ cm^?2, which is 4?10x lower than previously reported results.     

Growth of (GaAs)1_x(Ge2)x by metalorganic chemical vapor deposition

We report deposition of (GaAs)_{1_x}(Ge₂)_x on GaAs substrates over the entire alloy range. Growth was performed by metalorganic chemical vapor deposition at temperatures of 675 to 750°C, at 50 and 760 Torr, using trimethylgallium, arsine, and germane at rates of 2–10 μ/h. Extrinsic doping was achieved using silane and dimethylzinc in hydrogen. Characterization methods include double-crystal x-ray rocking curve analysis, Auger electron spectroscopy, 5K photoluminescence, optical transmission spectra, Hall-effect, and Polaron profiling. Results achieved include an x-ray rocking curve full-width at half maximum as narrow as 12 arc-s, Auger compositions spanning the alloy range from x = 0.03 to x = 0.94, specular surface morphologies, and 5K photoluminescence to wavelengths as long as 1620 nm. Undoped films are n type, with n ≈ 1 × 10¹⁷ cm⁻³. Extrinsic doping with silane and dimethylzinc have resulted in films which are n type (10¹⁷ to 10¹⁸ cnr⁻³) or p type (5 × 10¹⁸ to 1 × 10²⁰ cm⁻³). Mobilities are generally ≈ 50 cm²/V-s and 500 cm²/V-s, for p and n films, respectively.     

Oxygen and carbon incorporation in low temperature epitaxial Si films grown by rapid thermal chemical vapor deposition (RTCVD)

Using SIMS analysis, we have measured oxygen and carbon concentrations in epitaxial Si films grown between 550 and 900° C. The films were grown by rapid thermal chemical vapor deposition from SiH₄ as well as several different SiH₂Cl₂ sources. We have found that at low deposition temperatures (∼750° C or lower), oxygen incorporation is first dictated by source gas impurities and then by residual chamber gases. For the case of SiH₂Cl₂, which can have substantial oxygen content due to its reactivity with H₂O, oxygen concentrations of about 10²⁰ cm^-3 are typical at low deposition temperatures. SiH₄, however, can be obtained in higher purity, and oxygen concentrations of 10¹⁸ cm^-3 can be realized at low temperatures. At higher deposition temperatures (750-900° C), SiO volatilizes, leaving the films grown from all sources with low oxygen concentrations, typically less than 5 × 10¹⁷ cm^-3. Carbon incorporation is much less of a problem since it is present to a lesser extent both in the chamber background and in the source gases. Carbon levels less than or equal to 10¹⁸ cm^-3 can be obtained at all deposition temperatures greater than about 650° C. The performance ofp/n junctions is shown to degrade significantly for junctions grown below 850° C. We conclude that for growth of long lifetime Si films in the temperature range <800° C, that low residual H₂O partial pressures (<10^-10 Torr) are desired. Therefore, CVD chambers should be loadlocked and also capable of base pressures as low as about 10^-9 Torr.     

Critical conditions for SiGe island formation during Ge deposition on Si(100) at high temperatures

The strain relaxation during the Ge growth on Si(100) occurs vikia surface diffusion and Si-Ge intermixing at temperatures below 800 °C. The Ge diffusion into the Si substrate is an additional process at higher temperatures. We found that, if its rate is higher than the Ge deposition rate, the island formation is not realized. We determined the critical Ge deposition rate as a function of the temperature in the range of 840–960 °C, at which the dynamic equilibrium between the growth of islands and their decay through the diffusion takes place. The islands grown in the conditions close to the dynamic equilibrium are ordered with a distance between them of about 1 µm and they form a smoothed surface morphology. These are indicative of the surface layer strain uniformity. The islands have a SiGe composition which, in the direction parallel to the sample surface, is more uniform in comparison with the islands grown at lower temperatures. The results show that the use of high temperatures essentially improves the conditions for the heterostructure self-organization.