MOVPE growth of GaInP/GaAs hetero-bipolar-transistors using CBr4 as carbon dopant source

Carbon doping of GaAs with carbon tetrabromide (CBr₄) in low pressure MOVPE has been investigated and applied to the fabrication of GaInP/GaAs HBTs. Especially the hydrogen incorporation and the associated acceptor passivation has been studied. The hydrogen found in single GaAs:C layers is predominantly incorporated during cooling the sample under AsH₃ after growth, n-Type capping layers can block this H indiffusion and GaAs:C base layers in HBTs show much lower H concentrations than GaAs:C single layers without a cap. A further reduction of acceptor passivation is possible by optimization of the growth procedure. First HBTs processed from layers with a base that was doped using CBr₄ show promising DC and HF performance (β = 45, for 2 × 20 μm² devices).     

Growth of 1.55 μm DH laserstructures using TBAs and TBP in MOMBE

In a comparative study we have chosen TBAs and TBP as well as AsH₃ and PH₃ for the growth of InP/GaInAs(P) heterostructures for laser applications in a production metalorganic molecular beam epitaxy (MOMBE) system. The n-type doping was performed with Si from an effusion cell, whereas for the p-type doping Be and DEZn were utilized. InP layers using TBP under optimized cracking conditions exhibit excellent surface morphology with good electrical properties in the low 10¹⁵ cm⁻³ range of carrier concentrations. The MOMBE growth mechanism is not disturbed by the hydride replacement compound. This allows for a convenient replacement without losing calibration data from the hydride process. Broad-area DH laserstructures with GaInAsP (λ = 1.55 μm) active regions were grown with AsH₃/PH₃ and TBAs/TBP. Comparable threshold current densities in the range of 1.6-2.3 kA/cm² are achieved for the lasers, grown with both sets of precursors combined with DEZn source doping. These results are in good agreement with the standard set by the hydride MOVPE process.     

InAlAs/InGaAs/InP sub-micron HEMTs grown by CBE

The InAlAs/InGaAs/InP high electron mobility transistor (HEMT) lattice matched to InP offers excellent high frequency, low noise operation for MMICs and low-noise amplifiers. The InP channel in the InP/InAlAs HEMT offers the advantages of improved high field velocity and higher breakdown voltages (the potential for higher power applications) over InGaAs channel HEMTs. InAlAs has been grown for the first time by CBE using TMAA producing InGaAs/InAlAs and InP/InAlAs HEMTs. Sub-micron InGaAs/InAlAs HEMTs with planar Si doping have been fabricated with f_t values of 150 GHz and f_max values of 160 GHz. This device showed excellent pinch-off charateristics, with a maximum transconductance of 890 mS/mm. The planar doped InGaAs channel HEMT had a higher f_t than a similar uniformly doped device. However, the non-optimized structure of the planar doped device resulted in a large output conductance of 120 mS/mm, limiting f_max for that device. A sub-micron InP channel device was grown with a quantum well channel and double-sided planar Si doping. A sheet charge density of 4.4×10¹² cm^-2 and associated room temperature mobility of 2800 cm²/V·s were achieved; however, the saturation current was low. The most likely causes for this are diffusion of the planar doping beneath the channel and the poor quality of the InP on InAlAs interface at the bottom of the quantum well channel.     

MOMBE GaAs and AlGaAs for microelectronic devices

This paper reviews the state of the art of GaAs and AlGaAs materials and microelectronic devices grown by MOMBE (metalorganic molecular beam epitaxy) and related techniques. FET, HEMT and HBT devices have been grown using MOMBE and in the case of FETs and HBTs excellent device and MMIC power performance has been obtained. For example, MOMBE HBTs show current gains in excess of 100 and MMIC power HBT circuits are delivering 2 W of power at 8.5 GHz. We will examine device behavior and relate this to properties of the GaAs and AlGaAs materials.     

Growth of heavily C-doped GaAs/AlGaAs MQW structures by MOVPE for 2–3 μm normal incidence photodetectors

The growth and intersubband optical properties of high quality heavily doped p-type GaAs/AlGaAs multiple quantum well (MQW) structures are reported. The MQWs were fabricated by the atmospheric pressure metalorganic vapor phase epitaxy process using liquid CCl₄ to dope the wells with C acceptors (N_a ≈ 2 × 10¹⁹ cm⁻³). A constant growth temperature was maintained for the entire structure while different V/III ratios were used for the well and barrier regions. By this process it is possible to achieve both high C doping densities in the wells and to simultaneously obtain good quality AlGaAs barriers. Fourier transform infrared spectroscopy measurements on heavily doped 10-period MQW structures reveal a new absorption peak at 2 μm with an effective normal incidence absorption coefficient of 4000 cm⁻¹. Photocurrent measurements on mesa-shaped diodes show a corresponding peak at 2.1 μm. The photodiodes exhibit a symmetrical current-voltage characteristic and a low dark current, which are indicative of a high quality MQW structure and a well-controlled C doping profile. The 2 μm absorption represents the shortest wavelength ever reported for any GaAs/AlGaAs or InGaAs/AlGaAs MQW structure and should be very useful for implementing multicolor infrared photodetectors.     

A comparative study of GaAs- and InP-based HBT growth by means of LP-MOVPE using conventional and non gaseous sources

Low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) growth of carbon doped (InGa)P/GaAs and InP/(InGa)As heterojunction bipolar transistors (HBT) is presented using a non-gaseous source (ngs-) process. Liquid precursors TBAs/TBP for the group-V and DitBuSi/CBr₄ for the group-IV dopant sources are compared to the conventional hydrides AsH₃/PH₃ and dopant sources Si₂H₆/CCl₄ while using TMIn/TEGa in both cases. The thermal decomposition of the non gaseous sources fits much better to the need of low temperature growth for the application of carbon doped HBT. The doping behavior using DitBuSi/CBr₄ is studied by van der Pauw Hall measurements and will be compared to the results using Si₂H₆/CCl₄. Detailed high resolution X-ray diffraction (HRXRD) analysis based on 004 and 002 reflection measurements supported by simulations using BEDE RADS simulator enable a non-destructive layer stack characterization. InGaP/GaAs HBT structures designed for rf-applications are grown at a constant growth temperature of T_gr=600°C and at a constant V/III-ratio of 10 for all GaAs layers. P-type carbon concentrations up to P = 5·10¹⁹cm⁻³ and n-type doping concentrations up to N = 7·10¹⁸cm⁻³ are achieved. The non self-aligned devices (A_E = 3·10 μm²)_show excellent performance, like a dc-current gain of B_max = 80, a turn on voltage of V_offset = 110 mV (Breakdown Voltage V_CEBr,0 > 10 V), and radio frequency properties of f_T/f_max = 65 GHz/59 GHz.

In the non-gaseous source configuration the strong reduction in the differences of V/III-ratios and temperatures during HBT structure growth enable easier LP-MOVPE process control. This is also found for the growth InP/InGaAs HBT where a high dc-current gain and high transit frequency of f_T= 120 GHz are achieved.     

Growth of laser single-crystals Er:YVO4 by floating zone method

High optical quality Er³⁺:YVO₄ laser crystals have been grown by using the floating zone method (FZ). The spectroscopic properties and 3 μm lasing of Er³⁺:YVO₄ were investigated. It is found that the Er³⁺ concentration has a negative effect on the emission of the transition ⁴I_13/2→⁴I_15/2(1.55 μm ), and a positive effect on that of the ⁴I_11/2→⁴I_13/2 transition (2.68 μm). With direct upper-state pumping and a plane-concave cavity a self-terminating laser was achieved at the wavelength of 2.724 μm in the 30 at% Er³⁺ doped sample.     

Fabrication, spectroscopy and laser performance of Nd-doped lead-silicate glass fibers

The fabrication of a highly efficient Nd³⁺-doped single-mode fiber laser operating at 1.06 μm is described. The Nd₃₊ is introduced by doping Nd₂O₃ into a multicomponent (flint) lead-silicate glass host, Schott commercial optical glass F7. A fabrication technique for doping rare-earth evenly into commercial optical glasses is demostrated. Spectroscopic properties relevant to laser operation in the Nd³⁺-doped lead-silicate glass fibers were measured and the influence of Pb₂₊ ions on the spectral properties was analyzed. Owing to the long lifetime and large absorption and emission cross-sections of Nd₃₊ in this lead-silicate glass host, a high-performance Nd³⁺-doped lead-silicate fibre laser device operating at 1.06 μm has been successfully demonstrated.     

Growth of highly uniform InP/GaInAs/GaInAsP heterostructures by MOMBE for device integration

We report on the growth of highly uniform GaInAsP layers which can be achieved reproducibly over a long period. Quaternary layers with, e.g., λ_g=1.050 μm are obtained with a variation of the gap wavelength within ±1 nm over one wafer. For the run to run reproducibility nearly the same narrow tolerance band was measured. The effect of the substrate misorientation is briefly discussed. Finally we present the data of the fully MOMBE grown structure for the vertical integration of waveguides and photodiodes. Dark currents vary between 130–600 pA and the device capacity is below 100 fF for 10 V reverse voltage for the selected device geometry.     

MoS2/SnS异质结太阳能电池的模拟研究

硫化亚锡(SnS)是一种Ⅳ-Ⅵ族层状化合物半导体材料,其禁带宽度与太阳能电池最佳带隙1.5 eV非常接近,并且在可见光范围内光的吸收系数很大(α>10⁴ cm^-1),因此SnS是一种很有应用前景的材料。本文利用太阳能电池模拟软件wxAMPS模拟了MoS₂/SnS异质结太阳能电池,主要研究SnS吸收层的厚度、掺杂浓度和缺陷态等因素对太阳能电池性能的影响。研究发现:SnS吸收层最佳厚度为2 μm,最佳掺杂浓度为1.0×10¹⁵ cm^-3;同时高斯缺陷态浓度超过1.0×10¹⁵ cm^-3时,电池各项性能参数随着浓度的增加而减小,而带尾缺陷态超过1.0×10¹⁹ cm^-3·eV^-1时,电池性能才开始下降;其中界面缺陷态对太阳能电池影响比较严重,界面缺陷态浓度超过1.0×10¹² cm^-2时,开路电压、短路电流、填充因子和转换效率迅速下降。另外,通过模拟获得的转换效率高达24.87%,开路电压为0.88 V,短路电流为33.4 mA/cm²。由此可知,MoS₂/SnS异质结太阳能电池是一种很有发展潜力的光伏器件结构。     

Demonstration of the N2 carrier process for LP-MOVPE of III/V''s

The suitability of an N₂ carrier in LP-MOVPE of GaInAs/InP device structures and for the growth of (Al)GaInP is investigated for the first time. Al-free GaInAs/InP HEMTs and MSM photodetectors exhibit cutoff frequencies of f_t = 135 GHz and f_max = 200 GHz and a bandwidth of 16 GHz and responsivity of 0.27 A/W, respectively. AlGaInP and GaInP layers deposited using the optimized growth conditions showed excellent structural, optical and homogeneity properties. For example X-ray diffractograms with FWHMs as low as 15–16 arcsec for 1 μm thick layers and 300 K photoluminescence mappings over full 2 inch wafers with standard deviations of ±0.23 and ±0.26 nm were obtained for both materials.     

The growth of Si/SiGe/Si structures for heterojunction bipolar transistor by gas source molecular beam epitaxy

Three n–p–n Si/SiGe/Si heterostructures with different layer thickness and doping concentration have been grown by a home-made gas source molecular-beam epitaxy (GSMBE) system using phosphine (PH₃) and diborane (B₂H₆) as n-and p-type in situ doping sources, respectively. Heterojunction bipolar transistors (HBTs) have been fabricated using these structures and a current gain of 40 at 300 K and 62 at 77 K have been obtained. The influence of thickness and doping concentration of the deposited layers on the current gain of the HBTs is discussed.     

Heavily carbon-doped p-type InGaAs by MOMBE

Carbon-doped In_xGa_1−xAs layers (x=0−0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As₄) and solid indium (In) as sources of Ga, As and In, respectively. The carrier concentration is strongly affected by growth temperature and indium beam flux. Heavy p-type doping is obtained for smaller In compositions. The hole concentration decreases with the indium composition from 0 to 0.8, and then the conductivity type changes from p to n at x=0.8. Hole concentrations of 1.0×10¹⁹ and 1.2×10¹⁸ cm^-3 are obtained for x=0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped In_xGa_1−xAs by MBE. Preliminary results on carbon-doped GaAs/In_xGa_1−xAs strained layer superlattices are also discussed.     

Growth of carbon-doped base GaAs/AlGaAs HBT by gas-source MBE using TEG, TEA, TMG, AsH3, and Si2H6

High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI₂H₆ (n = 9 × 10¹⁷ cm^-3), and the base layer (92.5 nm) was doped with carbon from TMG (p = 4 × 10¹⁹ cm^-3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 10⁴ A/cm². The device characteristics of our carbon-doped HBTs were found to be stable under current stress.     

Non-linear As(P) incorporation in GaAs1−yPy on GaAs and InAs1−yPy on InP

We find anion incorporation into both GaAs_1−yP_y on GaAs and InAs_1−yP_y on InP during gas source molecular beam epitaxy (GSMBE) is not linearly related to the hydride gas fluxes within our reactor. The deviation from an ideal model, i.e., y = ƒ_P/(ƒ_P+ƒ_As), where As(P) is the flux of AsH₃ (PH₃), can be as large as a factor of two. GaAsP exhibits the largest degree of nonlinearity and incorporation is found to depend quadratically on the fluxes over a wide range of flux ratio. Significant deviations are also found for InAsP; however, anion incorporation can be modeled with y = ƒ_P/(ƒ_P+βƒ_As).     

Sb2O3掺杂BiFeO3-BaTiO3压电陶瓷的结构及电性能研究

采用传统固相烧结法合成了0.7BiFeO₃-0.3BaTiO₃+x%Sb₂O₃(质量分数)陶瓷(BFO-BTO+xSb, x=0.00~0.20),研究了Sb₂O₃掺杂对BFO-BTO陶瓷的晶相结构、介电、导电以及压电和铁电性能的影响,并对影响机理进行探讨。结果表明:Sb掺杂导致陶瓷的晶体结构由伪立方相向菱形相转化。Sb的B位取代增加了BFO-BTO+xSb陶瓷的铁电弛豫性,降低高温损耗,并使居里温度T_c有所降低。导电特性的研究表明,Sb掺杂改变了$V_O^×$和Fe²⁺的浓度,降低了电导率,但没有改变陶瓷的导电机制,其主要载流子是氧空位。Sb掺杂量x=0.05时,BFO-BTO+xSb陶瓷表现出最佳的综合电性能:d₃₃=213 pC/N,k_p=28.8%,Q_m=38,T_c=520 ℃,P_r =24.7 μC/cm²。     

Growth and spectral properties of Nd:LaVO4 crystal

This paper reports the growth and spectral properties of 3.5 at% Nd³⁺:LaVO₄ crystal with diameter of 20×15 mm² which has been grown by the Czochralski method. The spectral parameters were calculated based on Judd–Ofelt theory. The intensity parameters Ω_λ are: Ω₂=2.102×10⁻²⁰ cm², Ω₄=3.871×10⁻²⁰ cm², Ω₆=3.235×10⁻²⁰ cm². The radiative lifetime τ_r is 209 μs and calculated fluorescence branch ratios are: β₁(0.88μm)=45.2, β₂(1.06μm)=46.7, β₃(1.34μm)=8.1. The measured fluorescence lifetime τ_f is 137 μm and the quantum efficiency η is 65.6%. The absorption band at 808 nm wavelength has an FWHM of 20 nm. The absorption and emission cross sections are 3×10⁻²⁰ and 6.13×10⁻²⁰ cm², respectively.     

Viscosity matching of new PbF2–InF3–GaF3 based fluoride glasses and ZBLAN for high NA optical fiber

New multicomponent PbF₂–InF₃–GaF₃ bulk glasses have been investigated. They show lower phonon energy (540 cm⁻¹) in comparison with 580 cm⁻¹ for ZBLAN. Large PbF₂ concentration provided glasses with high refractive index up to 1.582 and the viscosity curves revealed an excellent thermal compatibility with ZBLAYN glass. A multimode fiber with a numerical aperture of 0.51, a loss of 0.85 dB/m at 1.3 μm was fabricated using the rotational casting method.     

Growth and properties of (Pb0.90La0.10)TiO3 thick films prepared by RF magnetron sputtering with a PbO buffer layer

The (Pb_0.90La_0.10)TiO₃ [PLT] thick films (3.0 μm) with a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering method. The PLT thick films comprise five periodicities, the layer thicknesses of (Pb_0.90La_0.10)TiO₃ and PbO in one periodicity are fixed. The PbO buffer layer improves the phase purity and electrical properties of the PLT thick films. The microstructure and electrical properties of the PLT thick films with a PbO buffer layer were studied. The PLT thick films with a PbO buffer layer possess good electrical properties with the remnant polarization (P_r=2.40 μC cm⁻²), coercive field (E_c=18.2 kV cm⁻¹), dielectric constant (ε_r=139) and dielectric loss (tan δ=0.0206) at 1 kHz, and pyroelectric coefficient (9.20×10⁻⁹ C cm⁻² K⁻¹). The result shows the PLT thick film with a PbO buffer layer is a good candidate for pyroelectric detector.     

Confinement of δ Be at the one monolayer level in GaAs

We investigate growth dependences to the planar confinement of Be near the 1 monolayer, ML, level when δ doped in GaAs. We examine concentration dependences on the rates of segregation and diffusion, as well as the effect of As₂, As₂ and AsH₃ overpressure on Be confinement during growth. Evidence from both chemical profiling and surface electron diffraction point to a Be surface dimerization process that drives dopant segregation.