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.     

The electrical, optical and crystalline properties of GaAs: C grown by GSMBE using TMG and AsH3 for application to HBTs

We report the results of a comprehensive study on the electrical, optical and crystalline properties of heavily carbon doped p-type (100) GaAs epilayers (p = 6.3 × 10¹⁸−1.3 × 10²⁰ cm^-3; THICKNESS = 250−420 nm) grown by gas source molecular beam epitaxy using trimethylgallium and arsine. X-ray analysis showed epilayer lattice contraction with a mismatch of δa/a = -1.8 × 10^-3 at p = 1.3 × 10²⁰ cm^-3. Room temperature photoluminescence peak energy shifted from 1.40 eV (p = 6.3 × 10¹⁸ cm^-3) to 1.37 eV (p = 1.3 × 10²⁰ cm^-3). Stokes Raman spectra showed two modes assigned as the unscreened LO phonon (292 cm^-1) and the low frequency branch of the coupled hole-plasmon-LO-phonon (266 cm^-1). Conservation of Raman scattering rules under all incident light configurations showed that the (100) GaAs:C epilayers were of high crystalline quality without the presence of faceting or other such crystalline defects. Annealing at 900°C for between 30 s to 45 min, resulted in a significant reduction in the hole concentration, lattice contraction and photoluminescence intensity for all epilayers. The implications of these results for the development of GaAs/AlGaAs HBTs are discussed.     

Growth of highly doped p-type ZnTe layers on GaAs using a nitrogen DC plasma cell

In this paper we report about the use of a DC plasma cell for nitrogen doping of ZnTe layers grown on GaAs substrates by molecular beam epitaxy (MBE). The samples, characterized by high resolution X-ray diffraction, photoluminescence and Hall measurements, show good crystalline quality and carrier concentrations as high as 1×10²⁰ cm^-3 with mobilities up to 30 cm²/V·s at room temperature. To our knowledge, this is the highest hole doping level reported so far in the literature for any wide-gap II–VI compound. The achieved hole concentration is one order of magnitude larger than values reported using an RF plasma source.     

The growth and physics of ultra-high-mobility two-dimensional hole gas on (311)A GaAs surface

We report on the molecular beam epitaxy growth of modulation-doped GaAs-(Ga,Al)As heterostructures on the (311)A GaAs surface using silicon as the acceptor. Two-dimensional hole gases (2DHGs) with low-temperature hole mobility exceeding 1.2×10⁶ cm² V⁻¹ s⁻¹ with carrier concentrations as low as 0.8×10¹¹ cm⁻² have been obtained. This hole mobility is the highest ever observed at such low densities by any growth technique. We also report the first observation of persistent photoconductivity in a 2DHG. An analysis of the number density and temperature dependence of the mobility leads us to conclude that the mobility is limited by phonon scattering above 4 K and interface scattering at lower temperatures.     

Atomic-scale controlled incorporation of ultrahigh-density Si doping sheets in GaAs

Delta-doped GaAs:Si with doping densities up to 4×10¹⁴ cm⁻² has been grown by molecular beam epitaxy (MBE) at a substrate temperature of 590°C. To promote an ordered incorporation and thus avoid clustering of Si atoms, vicinal GaAs(001) surfaces 2° misoriented towards (111)Ga were used and Si was supplied in pulses. As evidenced by real-time reflection high-energy electron diffraction (RHEED) measurements an ordered incorporation of Si atoms on Ga sites along the step edges takes place. Although the ordered (3×2) structure degrades at high coverages, unusual high sheet carrier concentrations are obtained by pulsed delta-doping for doping concentrations >10¹³ cm⁻², as revealed by Hall measurements. The surface conditions during GaAs overgrowth have a strong influence on the free electron concentration, too. Raman scattering by local vibration modes and secondary ion mass spectrometry (SIMS) measurements are used to show that this is related to segregation effects as well as to a modification of the site occupancy.     

Quantum transport measurements on Si δ- and slab-doped In0.53Ga0.47As grown by molecular beam epitaxy

A series of high quality δ-doped In_0.53Ga_0.47As samples have been grown lattice matched to InP with design doping densities in the range 2×10¹² to 5×10¹² cm⁻². Analysis of the individual sub-band densities deduced from the Shubnikov-De Haas effect shows that both spreading and amphoteric behaviour increase with doping density.     

Tin and tellurium doping of InAs using SnTe in molecular beam epitaxy (MBE)

Tin telluride (SnTe) was utilized as an n-type dopant in the MBE growth of InAs epitaxial layers on GaAs substrates. The highest carrier concentration obtained was 2.9 × 10¹⁹ cm^-3 and the carrier density could be varied over three orders of magnitude by changing the SnTe source temperature. The highest mobilities obtained were 16,900 and 23,300 cm²/V … s at 300 and 77 K, respectively, for carrier concentration of 5 × 10¹⁶ cm^-3. Both Sn and Te were incorporated in the layers as determined by secondary ion mass spectroscopy (SIMS) analysis and the total concentration of Sn and Te were the same as the carrier density in the layer.     

High-quality InP grown by chemical beam epitaxy

InP films were grown by chemical beam epitaxy using trimethylindium (TMI) and pure phosphine (PH₃) in a flow control mode with hydrogen as the carrier gas, with the TMI flow rate fixed at 3 SCCM. Substrate temperatures were varied between 505 and 580°C and V/III ratios from 3 to 9. InP layers with high optical quality (intense and narrow excitonic transition lines) and high crystalline quality (narrow and symmetric X-ray diffraction peaks) could be grown only within a narrow parameter window around a substrate temperature of 545°C (δT_s ≤ 25°C) and a V/III ratio of 5.5 (δ(V/III) ≤ 2). Carrier densities of 8 × 10¹⁴ cm^-3 with mobilities of 70000 cm²/V.s measured at 77 K were obtained for growth conditions close to the edge of this parameter window towards low V/III ratios. The growth rate of inP was also clearly at its maximum in the given parameter window. Leaving the window, by changing either the growth temperature or the V/III ratio, significantly decreased the growth rate. This reduced growth rate was accompanied by a degradation in the crystalline quality. We also demonstrate that for higher TMI flow the parameter window shifts to higher growth temperatures. The InP could be doped effectively with Si in the range from 9 × 10¹⁵ to 3 × 10¹⁸ cm^-3.     

Gettering properties of PrO2 in In0.53Ga0.47As LPE growth

Praseodymium oxide was used for the gettering of background impurities from the melt, during In_0.53Ga_0.47As/InP LPE growth. The low amount of PrO₂ in the growth solution enables one to prepare n-type In_0.53Ga_0.47As epitaxial layers with electron concentration in the range of 2 × 10¹⁴ to 2 × 10¹⁶ cm^-3 and electron mobilities of 11,000 and 8400 cm²/V·s, respectively. These results were achieved without long time baking of the melt; homogenization lasted only 1 h. The electrical parameters and photoluminescence spectra of the grown layers are presented.     

Comparative analysis of characteristics of Si, Mg, and undoped GaN

We have grown undoped, Si- and Mg-doped GaN epilayers using metalorganic chemical vapor deposition. The grown samples have electron Hall mobilities (carrier concentrations) of 798 cm²/V s (7×10¹⁶ cm⁻³) for undoped GaN and 287 cm²/V s (2.2×10¹⁸ cm⁻³) for Si-doped GaN. Mg-doped GaN shows a high hole concentration of 8×10¹⁷ cm⁻³ and a low resistivity of 0.8 Ω cm. When compared with undoped GaN, Si and Mg dopings increase the threading dislocation density in GaN films by one order and two orders, respectively. Besides, it was observed that the Mg doping causes an additional biaxial compressive stress of 0.095 GPa compared with both undoped and Si-doped GaN layers, which is due to the incorporation of large amount of Mg atoms (4–5×10¹⁹ cm⁻³).     

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 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.     

SiC epitaxial layer growth in a novel multi-wafer vapor-phase epitaxial (VPE) reactor

Experimental results are presented for SiC epitaxial layer growths employing a unique planetary SiC-VPE reactor. The high-throughput, multi-wafer (7×2″) reactor, was designed for atmospheric and reduced pressure operation at temperatures up to and exceeding 1600°C. Specular epitaxial layers have been grown in the reactor at growth rates ranging from 3–5 μm/h. The thickest layer grown to date is 42 μm thick. The layers exhibit minimum unintentional n-type doping of 1×10¹⁵ cm⁻³, and room temperature mobilities of 1000 cm²/V s. Intentional n-type doping from 5×10¹⁵ cm⁻³ to >1×10¹⁹ cm⁻³ has been achieved. Intrawafer layer thickness and doping uniformities (standard deviation/mean at 1×10¹⁶ cm⁻³) are typically 4 and 7%, respectively, on 35 mm diameter substrates. Moderately doped, 4×10¹⁷ cm⁻³, layers, exhibit 3% doping uniformity. Recently, 3% thickness and 10% doping uniformity (at 1×10¹⁶ cm⁻³) has been demonstrated on 50 mm substrates. Within a run, wafer-to-wafer thickness deviation averages 9%. Doping variation, initially ranging as much as a factor of two from the highest to the lowest doped wafer, has been reduced to 13% at 1×10¹⁶ cm⁻³, by reducing susceptor temperature nonuniformity and eliminating exposed susceptor graphite. Ongoing developments intended to further improve layer uniformity and run-to-run reproducibility, are also presented.     

Growth of GaAs/AlGaAs HBTs by MOMBE (CBE)

In this paper, we will discuss how the unique growth chemistry of MOMBE can be used to produce high speed GaAs/AlGaAs heterojunction bipolar transistors (HBTs). The ability to grow heavily doped, well-confined layers with carbon doping from trimethylgallium (TMG) is a significant advantage for this device. However, in addition to high p-type doping, high n-type doping is also required. While elemental Sn can be used to achieve doping levels up to 1.5×10¹⁹ cm^-3, severe segregation limits its use to surface contact layers. With tetraethyltin (TESn), however, segregation does not occur and Sn doping can be used throughout the device. Using these sources along with triethylgallium (TEG), trimethylamine alane (TMAA), and AsH₃, we have fabricated Npn devices with 2 μm×10 μm emitter stripes which show gains of ≥ 20 with either ƒ_t = 55 GHz and ƒ_max = 70 GHz or ƒ_t = 70 GHz and ƒ_max = 50 GHz, depending upon the structure. These are among the best RF values reported for carbon doped HBTs grown by any method, and are the first reported for an all-gas source MOMBE process. In addition, we have fabricated a 70 transistor decision circuit whose performance at 10 Gb/s equals or exceeds that of similar circuits made from other device technologies and growth methods. These are the first integrated circuits reported from MOMBE grown material.     

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。     

Growth of semi-insulating InP by GSMBE

Fe doped semi-insulating InP layers have been grown by gas source MBE with a solid iron source. Structure as n-i-n, p-i-n and p-n-i-n were characterized by I(V) measurements and secondary ion mass spectroscopy profiling (SIMS). As shown by SIMS, uniform Fe doping and abrupt transitions are achieved for the different structures studied. Resistivities as high as 1.5×10⁹ Ω cm are determined from I(V) curves for Fe concentrations in the 10¹⁷ cm^-3 range. Lasers with semi-insulating layers have been realized for the first time by gas source MBE. Preliminary results show power emission of 43 mW, without antireflecting coating, comparable to state-of-the-art characteristics.     

单层n型MoS2/p型c-Si异质结太阳电池数值模拟

单层二硫化钼(MoS₂)是一种具有优异光电性能的半导体材料,在太阳能能量转换中表现出很大的应用潜力。本文基于AMPS模拟软件,对单层n型MoS₂/p型c-Si异质结太阳电池进行了数值模拟与分析。通过模拟优化,n型MoS₂的电子亲和能为3.75 eV、掺杂浓度为10¹⁸ cm^-3,p型c-Si的掺杂浓度为10¹⁷ cm^-3时,太阳电池能够取得最高22.1%的转换效率。最后模拟了n型MoS₂/p型c-Si异质结界面处的界面态对太阳电池性能的影响,发现界面态密度超过10¹¹ cm^-2·eV^-1时会严重影响太阳电池的光伏性能。     

Se-doped AlGaAs grown on GaAs(111)A by molecular beam epitaxy

The electrical properties of Se-doped Al_0.3Ga_0.7As layers grown by molecular beam epitaxy (MBE) on GaAs(111)A substrates have been investigated by Hall-effect and deep level transient spectroscopy (DLTS) measurements. In Se-doped GaAs layers, the carrier concentration depends on the misorientation angle of the substrates; it decreases drastically on the exact (111)A surface due to the re-evaporation of Se atoms. By contrast, in Se-doped AlGaAs layers, the decrease is not observed even on exact oriented (111)A. This is caused by the suppression of the re-evaporation of Se atoms, by Se---Al bonds formed during the Se-doped AlGaAs growth. An AlGaAs/GaAs high electron mobility transistor (HEMT) structure has been grown. The Hall mobility of the sample on a (111)A 5° off substrate is 5.9×10⁴ cm²/V·s at 77 K. This result shows that using Se as the n-type dopant is effective in fabricating devices on GaAs(111)A.     

Ion implantation effects in heavy metal fluoride glasses

Samples of a heavy metal fluoride glass (BInZnYbTGa) were subjected to argon and nitrogen irradiations of energies of 50 and 100 keV and fluences of 5×10¹⁶ and 1×10¹⁷ ions/cm². A 10 keV Ar irradiation at the ion dose of 1×10¹⁷/cm² was also performed. Modifications induced by the implants were characterized by nuclear microanalysis, electron spectroscopy, scanning electron microscopy and optical techniques. Surface precipitation of Th and Ba, as well as F and In depletion, were detected. Correlated modifications of the optical transmittance and reflectance were observed.     

New aluminium precursors for MOMBE (CBE): a comparative study

Recently different new Al precursors have been developed to improve the electrical and optical quality of AlGaAs layers grown by MOMBE (CBE), since AlGaAs layers still suffer from the high incorporation of oxygen and carbon. Three approaches are introduced and results obtained from Al_xGa_1−xAs layers (0 < x ≤ 1) are discussed. APAH, a double ring structure molecule, was found to yield AlGaAs layers with high contents of carbon and nitrogen. The use of an Alane-adduct decreases impurity concentrations and improves optical properties. However, TIBAl is superior and provides highest PL response together with carrier concentrations below p = 10¹⁶ cm^-3. Even though the concept of coordinative saturation is promising, results achieved by TIBAl showed that trialkyls could also be well suited for AlGaAs, assuming that they are properly synthesized.