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1.
Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, xBi, lower than 0.2 at.%, an excess deep-donor level (activation energy Ed≈0.03–0.04 eV) appears, and Hall mobility is low. In contrast, for xBi>0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 1017 cm−3. Inductive coupled plasma (ICP) emission analysis shows that, for xBi=1 at.%, Bi concentration in the epitaxial layer is as high as NBi=2.3–2.7 × 1019 cm−3. These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bi-doped layers shows a minimum at a Te vapor pressure of 2.2 × 10−5 torr for growth temperature 470°C, which is coincident with that of the undoped PbTe.  相似文献   

2.
GaN epitaxial layers were grown on sapphire substrates in a separate-flow reactor by metalorganic chemical vapor deposition. The flow-rate ratio of H2 on the upper stream to NH3 on the bottom stream is varied from 0.5 to 2. The growth condition and characterization of the GaN epitaxial layers are investigated in detail. The H2 flow rate of the upper stream strongly affects the reactant gas flow pattern near the substrate surface and thus influences the quality of epitaxial layers. At the optimum H2/NH3 flow ratio of 1.0, we can obtain a good quality of GaN epitaxial layers which exhibit a strong near band-edge emis-sion in the 20 K photoluminescence (PL), a full width at half maximum of 66 meV for the 300 K PL, an electron mobility of 266 cm2/V-s and concentration of 1 × 1018 cm−3 at 300 K.  相似文献   

3.
The structure and crystal quality of epitaxial films of SiC/AlN/6H-SiC(0001) prepared by chemical vapor deposition were evaluated by high resolution transmission electron microscopy (HRTEM) and x-ray diffraction techniques. Cross-sectional HRTEM revealed an abrupt AlN layer-6H-SiC substrate junction, but the transition between the AlN and SiC layers was much rougher, leading to the formation of a highly disordered SiC region adjacent to the interface. The AlN layer was relatively defect free, while the SiC layer contained many microtwins and stacking faults originating at the top SiC/AlN interface. The SiC layer was the 3C-polytype, as determined by double crystal x-ray rocking curves. The SiC layers were under in-plane compressive stress, with calculated defect density between 2–4×107 defects/cm−2.  相似文献   

4.
Donor ion-implantation doping into SiC   总被引:1,自引:0,他引:1  
In this paper, dopant electrical activation and dopant thermal stability results of As and Sb-implanted 6H-SiC epitaxial layers and N ion implantations into bulk semi-insulating (SI) 4H-SiC are presented. In addition, empirical formulas for the first four statistical moments (range, straggle, skewness, and kurtosis) of the implant depth distributions of N and P ion implants are developed in the energy range of 50 keV to 4 MeV. The nitrogen ion-implantations in SI 4H-SiC yield an acceptable (27%) room-temperature electrical activation (ratio of measured sheet carrier concentration at room-temperature to the implant dose) for N concentrations of 2×1019 cm−3. The As and Sb implants out-diffuse during annealing and yield low (<20%) room-temperature electrical activation for implant concentrations of 1019 cm−3. The N and P implant depth distributions in SiC can be simulated using the Pearson IV distribution function and the range statistics provided by the empirical formulas.  相似文献   

5.
This paper focuses on growth of 4H−SiC epitaxial layers using the hot-wall CVD technique. The relation between the growth regime like total flow, system pressure, C/Si ratio and growth temperature and the characteristics of nominally undoped epilayers, such as thickness uniformity and background doping concentration have been investigated. The epitaxial layers were investigated by optical microscopy, capacitance-voltage measurements, x-ray rocking curve maps, electron channelling patterns and secondary ion mass spectroscopy. Layers up to 40 μm in thickness with a variation of about ±4% and with residual n-type doping levels in the low 1014 cm−3 ranges have been obtained on Si faces wafers. SIMS measurements have shown that the impurity concentration of acceptors like B and Al is below 2×1014 cm−3.  相似文献   

6.
The polytype and surface and defect microstructure of epitaxial layers grown on 4H(), 4H(0001) on-axis, 4H(0001) 8° off-axis, and 6H(0001) on-axis substrates have been investigated. High-resolution x-ray diffraction (XRD) revealed the epitaxial layers on 4H() and 4H(0001) 8° off-axis to have the 4H-SiC (silicon carbide) polytype, while the 3C-SiC polytype was identified for epitaxial layers on 4H(0001) and 6H(0001) on-axis substrates. Cathodoluminescence (CL), Raman spectroscopy, and transmission electron microscopy (TEM) confirmed these results. The epitaxial surface of 4H() films was specular with a roughness of 0.16-nm root-mean-square (RMS), in contrast to the surfaces of the other epitaxial layer-substrate orientations, which contained curvilinear boundaries, growth pits (∼3 × 104 cm−2), triangular defects >100 μm, and significant step bunching. Molten KOH etching revealed large defect densities within 4H() films that decreased with film thickness to ∼106 cm−2 at 2.5 μm, while cross-sectional TEM studies showed areas free of defects and an indistinguishable film-substrate interface for 4H() epitaxial layers.  相似文献   

7.
In a low-pressure metalorganic vapor phase epitaxy process, we used dc-plasma activated nitrogen to dope ZnSe, grown with ditertiarybutylselenide and dimethylzinc-triethylamine. The nitrogen concentration of up to 2 × 1018 cm−3 in the doped layers can be adjusted by the growth temperature, the dc-plasma power, and the N2 dopant flow. Due to the high n-type background carrier concentration of the order of 1017 cm−3 in undoped samples, the doped layers show n-type conductivity or were semi-insulating because of an additional compensation by hydrogen incorporated with a concentration of the order of 1018 cm−3. A planar doping scheme was applied to reduce this hydrogen incorporation by one order of magnitude, although H2 was used as carrier gas.  相似文献   

8.
Carbon dopedp-type GaAs and In0.53Ga0.47As epitaxial layers have been grown by low-pressure metalorganic chemical vapor deposition using CC14 as the carbon source. Low-temperature post-growth annealing resulted in a significant increase in the hole concentration for both GaAs and In0.53Ga0.47As, especially at high doping levels. The most heavily doped GaAs sample had a hole concentration of 3.6 × 1020 cm−3 after a 5 minute anneal at ≈400° C in N2, while the hole concentration in In0.53Ga0.47As reached 1.6 × 1019 cm−3 after annealing. This annealing behavior is attributed to hydrogen passivation of carbon acceptors. Post-growth cool-down in an AsH3/H2 ambient was found to be the most important factor affecting the degree of passivation for single, uncapped GaAs layers. No evidence of passivation is observed in the base region of InGaP/GaAs HBTs grown at ≈625° C. The effect ofn-type cap layers and cool-down sequence on passivation of C-doped InGaAs grown at ≈525° C shows that hydrogen can come from AsH3, PH3, or H2, and can be incorporated during growth and during the post-growth cool-down. In the case of InP/InGaAs HBTs, significant passivation was found to occur in the C-doped base region.  相似文献   

9.
Direct current measurements are performed up to 673K at circular and linear (shown in parenthesis) enhancement-mode metal oxide semiconductor field effect transistors (MOSFETs). These devices are fabricated on a p-type 6H-SiC epitaxial layer with a doping concentration NA ≈ 1 × 1016 cm−1. The n+ source/drain regions and the p+ regions for the channel stops are achieved by ion implantation of nitrogen and aluminum, respectively. Both MOSFET geometries show excellent output characteristics with a good saturation behavior even at elevated temperatures. The inversion layer mobility μn extracted in the linear region is 38 cm2·V−1·s−1 (35 cm2·V−1·s−1) and reveals a weak dependence on temperature with a maximum of 46 cm2·V−1·s−1 (42 cm2·V−1·s−1) at about 473K. Regarding the transfer characteristics, the drain current ID can be well modulated by the gate-source voltage VGS resulting in an Ion/Loff-ratio of 108 (108) at 303K and 105 (106) at 673K. In the subthreshold regime, ID can be pinched off well below 10 pA with a subthreshold swing of 150 mV/decade (155 mV/decade) at room temperature. The threshold voltage VT as a function of temperature shows two linear sections with negative temperature coefficients of −6.8 mV·K−1 (−6.8 mV·K−1) from 303 to 423K and −2.5 mV·K−1 (−2.0 mV·K−1) from 423 to 673K. By measuring VT as a function of bulk-source voltage VBS at different temperatures, NA can be directly estimated at a transistor and gives 9.6 × 1015 cm−3 (9.8 × 1015 cm−3). The measured bulk Fermi potential Φf of the p-type epitaxial layer deviates less than 10% from the calculated value at a given temperature.  相似文献   

10.
The liquid phase epitaxial growth of high purity InGaAs layers lattice matched to InP has been studied using rare earth dysprosium (Dy) as an impurity getter. Using this getter, the electron concentration decreased from 1.2 × 1018 cm−3 to 1 × 1015 cm−3 while the mobility at 300K increased from 3920 to 10200 cm2/V-s. The epilayers were characterized by resistivity, Hall effect, electrochemical capacitance-voltage profiling, photoluminescence, secondary ion mass spectroscopy, double crystal x-ray diffractometry, and deep level transient spectroscopy (DLTS). Significant improvement was observed in both electrical and optical properties of the layers with an increasing amount of Dy in the melt. The amount of Dy was thus optimized (6 × 10−4 atomic fraction) for the highest purity layer. The major background impurity was identified as silicon. The gettering of both acceptors, as well as donors, by Dy was established and gettering of oxygen was confirmed for the first time through DLTS studies.  相似文献   

11.
The growth of epitaxial layers of mercury-cadmium-telluride (Hg1-xCdxTe) with relatively low x (0.2-0.3) from Te-rich solutions in an open tube sliding system is studied. The development of a semiclosed slider system with unique features permits the growth of low x material at atmospheric pressure. The quality of the films is improved by the use of Cd1-yZyTe and Hg1-xCdxTe substrates instead of CdTe. The substrate effects and the growth procedure are discussed and a solidus line at a relatively low temperature is reported. The asgrown epitaxial layers are p-type with hole concentration of the order of 1·1017 cm−3, hole mobility of about 300 cm2·V−1 sec−1 and excess minority carrier life-time of 3 nsec, at 77 K.  相似文献   

12.
Liquid phase epitaxial growth of InAsxSb1−x, for 0<x<0.27 and In1−yGaySb, for 0<y<0.37, has been successfully accomplished on (111)B InSb substrates between the temperatures of 450 and 520°C. The phase diagrams and the growth conditions for high-quality planar epitaxial layers have been determined. For growth of InAsxSb1−x for high values of x, the strong tendency of the ternary melt to dissolve the substrate, even when the liquid is a few degrees below its melting point, was negated by using large supercooling. Small supercooling of zero to 5.6°C were required over the whole range of composition examined for (In.Ga)Sb, whereas, for example, supercooling greater than 30°C was required to grow InAso.26Sbo.74 to avoid substrate dissolution. Lattice mismatch to the substrate was relieved by compositional grading. Etch pit studies in both materials yielded dislocation densities ranging from 5.8 × 102 to 2×106 cm−2 with most materials in the low 104 range. Hall and resistivity measurements performed at 300K and 77K on most samples showed an impurity contamination of the epitaxial layers. Some samples were n-type (carrier concentration approximately 1017/cm3), with varying degrees of acceptor compensation and others were n-type (carrier concentration approximately l017/cm3) at room temperature due to intrinsic conduction, but exhibited p-type conduction (carrier concentration approximately 5×l0l6/cm3) at 77K. Hall measurements performed on one of the latter samples ofvery low As content from 77K to 4.2K to examine hole freeze-out yielded an acceptor level ionization energy of 0.0126eV which is close to the effective mass acceptor level ionization energy in InSb. The electron-to-hole mobility ratio was also found to be 65.9. Electron microprobe analysis showed silicon to be the dominant impurity.  相似文献   

13.
We have studied the p-type doping in ZnSe molecular beam epitaxial growth using a novel high-power (5 kW) radio frequency (rf) plasma source. The effect of growth conditions such as the rf power, the Se/Zn flux ratio and the growth temperature on p-ZnSe:N was investigated. The net acceptor concentration (NA—ND) of around 1 × 1018 cm−3 was reproducibly achieved. The activation ratio ((NA—ND)/[N]) of p-ZnSe:N with NA—ND of 1.2 × 1018 cm−3 was found to be as high as 60%, which is the highest value so far obtained for NA—ND ∼ 1018 cm−3. The 4.2K photoluminescence spectra of p-ZnSe:N grown under the optimized growth condition showed well-resolved deep donor-acceptor pair emissions even with high NA—ND. On leave from Sumitomo Electric Industry Ltd. On leave from Sony Corp.  相似文献   

14.
We have grown AlxIn1−xSb epitaxial layers by metalorganic chemical vapor deposition using tritertiarybutylaluminum (TTBAl), trimethylindium (TMIn), and triethylantimony (TESb) as sources in a high speed rotating disk reactor. Growth temperatures of 435 to 505°C at 200 Torr were investigated. The V/III ratio was varied from 1.6 to 7.2 and TTBAl/(TTBAl+TMIn) ratios of 0.26 to 0.82 were investigated. AlxIn1−xSb compositions from x=0.002 to 0.52 were grown with TTBAl/(TTBAl+TMIn) ratios of 0.62 to 0.82. Under these conditions, no Al was incorporated for TTBAl/(TTBAl+TMIn) ratios less than 0.62. Hall measurements of AlxIn1−xSb showed hole concentrations between 5×1016 cm−3 to 2 × 1017 cm−3 and mobilities of 24 to 91 cm2/Vs for not intentionally doped AlxIn1−xSb.  相似文献   

15.
Semi-insulating 4H-SiC ⟨0001⟩ wafers have been phosphorus ion implanted at 500°C to obtain phosphorus box depth profiles with dopant concentration from 5 × 1019 cm−3 to 8 × 1020 cm−3. These samples have been annealed by microwave and conventional inductively heated systems in the temperature range 1700°C to 2050°C. Resistivity, Hall electron density, and Hall mobility of the phosphorus-implanted and annealed 4H-SiC layers have been measured in the temperature range from room temperature to 450°C. The high-resolution x-ray diffraction and rocking curve of both virgin and processed 4H-SiC samples have been analyzed to obtain the sample crystal quality up to about 3 μm depth from the wafer surface. For both increasing implanted phosphorus concentration and increasing post-implantation annealing temperature the implanted material resistivity decreases to an asymptotic value of about 1.5 × 10−3 Ω cm. Increasing the implanted phosphorus concentration and post-implantation annealing temperature beyond 4 × 1020 cm−3 and 2000°C, respectively, does not bring any apparent benefit with respect to the minimum obtainable resistivity. Sheet resistance and sheet electron density increase with increasing measurement temperature. Electron density saturates at 1.5 × 1020 cm−3 for implanted phosphorus plateau values ≥4 × 1020 cm−3, irrespective of the post-implantation annealing method. Implantation produces an increase of the lattice parameter in the bulk 4H-SiC underneath the phosphorus-implanted layer. Microwave and conventional annealing produce a further increase of the lattice parameter in such a depth region and an equivalent recovered lattice in the phosphorus-implanted layers.  相似文献   

16.
The epitaxial layers of Hg1−xCdxTe (0.17≦×≦0.3) were grown by liquid phase epitaxy on CdTe (111)A substrates using a conventional slider boat in the open tube H2 flow system. The as-grown layers have hole concentrations in the 1017− 1018 cm−3 range and Hall mobilities in the 100−500 cm2/Vs range for the x=0.2 layers. The surfaces of the layers are mirror-like and EMPA data of the layers show sharp compositional transition at the interface between the epitaxial layer and the substrate. The effects of annealing in Hg over-pressure on the properties of the as-grown layers were also investigated in the temperature range of 250−400 °C. By annealing at the temperature of 400 °C, a compositional change near the interface is observed. Contrary to this, without apparent compositional change, well-behaved n-type layers are obtained by annealing in the 250−300 °C temperature range. Sequential growth of double heterostructure, Hgl−xCdxTe/Hgl−yCdyTe on a CdTe (111)A substrate was also demonstrated.  相似文献   

17.
High-quality AIGaAs epilayers have been grown by low pressure organometallic vapor phase epitaxy with a new aluminum precursor tritertiarybutylaluminum (TTBAl). Layers grown at 650°C have a featureless mirror surface morphology and strong room temperature photoluminescence. Carbon was not detectable in chemical analysis by secondary ion mass spectroscopy, nor in low temperature (4K) photoluminescence spectra. Oxygen concentration in Al0.25Ga0.75As is as low as ∼2−3 × 1017 cm−3. Nominally undoped AIGaAs layers exhibit n-type conductiv-ity with electron concentrations at ∼ 1−1.5 × 1016 cm−3. A high degree of compo-sitional uniformity over 5 cm diam substrates (0.268 ±0.001) was obtained. These results indicate the potential for TTBA1 as an aluminum precursor for low temperature growth of Al-containing III-V alloys.  相似文献   

18.
We demonstrate peak fT and fmax of 50 GHz for heterojunction bipolar transistors (HBTs) with an oxygen concentration in the epitaxial SiGe base layer of about 1020 cm−3. These fT/fmax values are over 10 GHz higher than for identically processed HBTs with an O content of only 1018 cm−3. This is due to reduced transient enhanced diffusion of boron in the O-rich layers. However, the base carrier lifetimes are reduced by the high oxygen content. We show that ideal base current characteristics and a low 1/fnoise level can be obtained despite this effect by localizing the emitter-base space-charge region outside the O-rich layer.  相似文献   

19.
Room-temperature Fourier transform infrared reflection (FTIR) spectroscopy was carried out on heavily and lightly doped 4H-SiC films grown by chemical vapor deposition on conducting, n-type (nitrogen) doped substrates. A model-based curve fit of the experimentally observed reflectance spectra from these samples is performed using a dielectric function that accounts for the phononphoton coupling and plasmon-photon coupling. The value of the longitudinal-optical (LO) phonon frequency estimated from the reflectance spectrum in the range 600–1,200 cm−1 is observed to increase in direct correlation with the electron free-carrier concentration (FCC). This shift reflects phonon-plasmon coupled modes. The shift from the undisturbed ωLO observed, for example, in semi-insulating SiC is exploited to improve the model-based estimation of epi parameters such as thickness and doping in cases where the free-carrier concentration is less than about 2×1018 cm−3.  相似文献   

20.
In this work, heavily aluminum (Al)-doped layers for ohmic contact formation to p-type SiC were produced by utilizing the high efficiency of Al incorporation during the epitaxial growth at low temperature, previously demonstrated by the authors’ group. The low-temperature halo-carbon epitaxial growth technique with in situ trimethylaluminum (TMA) doping was used. Nearly featureless epilayer morphology with an Al atomic concentration exceeding 3 × 1020 cm−3 was obtained after growth at 1300°C with a growth rate of 1.5 μm/h. Nickel transfer length method (TLM) contacts with a thin adhesion layer of titanium (Ti) were formed. Even prior to contact annealing, the as-deposited metal contacts were almost completely ohmic, with a specific contact resistance of 2 × 10−2 Ω cm2. The specific contact resistance was reduced to 6 × 10−5 Ω cm2 by employing a conventional rapid thermal anneal (RTA) at 750°C. Resistivity of the epitaxial layers better than 0.01 Ω cm was measured for an Al atomic concentration of 2.7 × 1020 cm−3.  相似文献   

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