Chemical beam epitaxy

Chemical beam epitaxy (CBE), an offshoot of molecular-beam epitaxy (MBE) and metalorganic chemical vapor deposition (MO-CVD), is described. It combines the beam nature of MBE and the control and use of all-vapor source as in MO-CVD. The growth kinetics of all three processes are examined, and their advantages and disadvantages are considered. The monolayer thickness control capabilities of CBE are highlighted. Device applications of CBE are discussed     

化学束外延及其在半导体材料与器件中的应用

本文介绍了薄膜晶体生长的最新技术--化学束外延(CBE),通过与分子束外延(MBE)和金属有机化学汽相沉积(MOCVD)技术的比较,说明了这一新技术的基本概念,生长动力学以及在半导体材料和激光器件方面的应用.     

Growth and characterization of Ga2Te3 films by metalorganic molecular beam epitaxy

Single-crystal Ga2Te3 films were grown by metalorganic moleular beam epitaxy (MOMBE). The crystallinity of the Ga2Te3 films was characterized by reflection high energy electron diffraction (RHEED) and x-ray diffraction measurements. Unique substrate temperature and VI/III ratio dependence of crystallinity and growth rate are obtained in this experiment for the first time.     

Delta-doping interband tunneling diode by metal-organic chemicalvapor deposition

A delta-doped InGaAs-GaAs quantum well (QW) has been grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The full width at half maximum (FWHM) of the doping profile analyzed by capacitance-voltage measurements is less than 30 A and is comparable to those produced by molecular beam epitaxy (MBE) or chemical beam epitaxy (CBE). Two kinds of delta-doping interband tunneling diodes with band diagrams similar to those of InAs/AlSb-GaSb related interband tunneling diodes have been fabricated     

GaInAs/InP waveguide multiple-quantum-well optical modulator with 9 dB on/off ratio

Clear excitonic peak wavelength shifts are obtained with an applied electric field and large on/off ratio optical modulation of long-wavelength light propagating along the plane of GaInAs/InP multiple-quantum-well (MQW) structures grown by metalorganic molecular beam epitaxy (MOMBE). These waveguide MQW optical modulators have a modulation on/off ratio of 8:1 (9 dB) at a driving voltage as low as 5 V operating at a wavelength of 1.55 ?m. This measurement is the first step towards faster and higher extinction ratio devices.     

Anisotropic surface diffusion at crystal facet transitions during localized Ga---In---As---P growth by MOMBE

Localized grown InP/GaInAs(P) heterostructure ridges by selective area metalorganic molecular beam epitaxy (MOMBE) are investigated concerning the surface diffusion. The structures have different crystal facets at the semiconductor mask transition area. The surface diffusion processes between these simultaneously growing facets are a function of the step density, which is preset by the selected substrate misorientations. The anisotropic surface diffusion in the direction of the group V terminated surface steps determines the lateral facet growth and leads to a fine oscillating surface corrugation on the ridge surface only near the step upwards oriented facet transition. A simulation of this anisotropic surface corrugation by a deterministic nonlinear partial differential equation of a one dimensional diffusion model for the selective area growth in MOMBE presents a good agreement with the measured corrugation depth and periods.     

Selective area epitaxy and growth over patterned substrates by chemical beam epitaxy

Selective area epitaxy and growth over patterned substrate using chemical beam epitaxy (CBE) were investigated. Truly selective area epitaxy with no deposition over the SiO/sub 2/ masks has been routinely obtained with excellent epilayer morphology. Uniform coverage was obtained for regrowth over etched mesas to form buried heterostructures. For growth over etch channels, very unique growth characteristics were obtained. Buried crescent stripes similar to those formed by liquid-phase epitaxy inside channels were also obtained by CBE. These growth characteristics demonstrated the unique of CBE for diode laser fabrication.<>     

The growth of GaAs,AIGaAs, InP and InGaAs by chemical beam epitaxy using group III and V alkyls

The growth kinetics of chemical beam epitaxy (CBE) were investigated with the growth of GaAs, AIGaAs, InP, and InGaAs. Results obtained with epilayers grown by using trimethylarsine (TMAs) and triethylphosphine (TEP) instead of arsine (AsH3) and phosphine (PH₃) were reviewed with some additional results. The CBE grown epilayers have similar optical quality to those grown by molecular beam epitaxy (MBE). Superlattices of GaAs/AlGaAs with abrupt interfaces have been prepared. Since trimethylindium (TMIn) and triethylgallium (TEGa) used in the growth of InGaAs emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the InGaAs epilayers grown. Lattice-mismatch Δα/α< 1 x 10^-3 have been reproducibly obtained. For epilayers grown with high purity TMAs source, room-temperature electron mobility as high as 9000 cm²/V sec and concentrations of ˜7 x 10¹⁵ cm^-3 were produced. In general, the electron mobilities were as good as those obtained from low-pressure metalorganic chemical vapor deposition. (MO-CVD). Unlike MBE, since the In and Ga were derived by the pyrolysis of TMIn and TEGa molecules at the heated substrate surface, respectively, oval defects observed in MBE grown epilayers due to Ga splitting from Ga melt were not present in CBE grown epilayers. This is important for integrated circuit applications. Unlike MO-CVD, the beam nature of CBE allows for selective area growth of epilayers with well-defined smooth edges using mask shadowing techniques. Typically, growth rates of 2-5μm/h for InP, 2-6μm/h for GaAs and AIGaAs, and 2-5μm/h for InGaAs were used.     

Dopant incorporation in GaAs and AlGaAs grown by MOMBE for high speed devices

Continued improvement in GaAs/AlGaAs device technology requires higher doping levels, both to reduce parasitics such as source resistances, and to enhance speed in devices such as the heterostructure bipolar transistor (HBT). In this paper we will discuss doping issues which are critical to high speed performance. In particular, we will focus on doping of GaAs and AIGaAs using carbon as the acceptor and Sn as the donor. Due to the unique growth chemistry of metalorganic molecular beam epitaxy (MOMBE), both of these impurities can be used to achieve high doping levels when introduced from gaseous sources such as trimethylgallium (TMG) or tetraethyltin (TESn). Comparison of SIMS and Hall measurements show that both elements give excellent electrical activation to 1.5 × 10¹⁹ cm³ for Sn and 5 × 10²⁰ cm⁻³ for C. More importantly, we have found that both impurities canbe used to achieve high quality junctions, indicating that little or no diffusion or segregation is occurring during growth. Because of the excellent incorporation behavior of these dopants, we have been able to fabricate a wide range of devices including field effect transistors (FETs), high electron mobility transistors (HEMTs), and Pnp HBTs whose performance equals or exceeds that of similar devices grown by other techniques. In addition to these results, we will briefly discuss the key differences in growth kinetics which allow such abruptness and high doping levels to be achieved more readily in MOMBE than in other growth techniques.     

The role of ion characteristics in determining the structural and electrical quality of InN grown by metalorganic molecular beam epitaxy

The effects of growth temperature and nitrogen plasma biasing on the electrical and structural properties of InN grown using electron cyclotron resonance metalorganic molecular beam epitaxy (ECR MOMBE) have been investigated. These results are compared to those found from InN grown using a higher energy radio frequency (rf) plasma source (rf MOMBE). By varying the bias of the nitrogen plasma or the growth temperature, it is possible to achieve smooth surface morphologies. However, biasing can also be used to increase the mobility by a factor of two while the growth temperature has only a small effect. By contrast, use of an rf plasma improves mobility by nearly a factor of ten. None of the growth conditions investigated were found to significantly alter the electron concentration, which was measured to be 1−5 × 10²⁰ cm⁻³.     

Simultaneous in situ measurement of film thickness and temperatureby using multiple wavelengths pyrometric interferometry (MWPI)

Film thickness and temperature are two of the most important quantities in semiconductor manufacturing. They play a fundamental role in many standard production techniques like chemical vapor deposition (CVD, LPCVD, PECVD), thermal oxidation and diffusion. They are especially important for more recently developed technologies like molecular beam epitaxy (MBE), metal organic MBE (MOMBE), metal organic CVD (MOCVD), chemical beam epitaxy (CBE), etc. In this paper, an optical in situ method for simultaneous film thickness and temperature measurements-named multiple wavelengths pyrometric interferometry (MWPI)-is introduced, which is capable of high resolution (up to 0.1 nm for thickness and 0.025 K for temperature) and for real time data evaluation. It can be used for process control as well as in situ quality inspection without time delay or additional handling mechanisms and is suitable for monitoring single films as well as multilayer structures. MWPI is insensitive to vibration, rotation and misalignment of the wafer. Due to its optical basis it is also insensitive to hostile environments like high temperature and/or chemical reactive gases     

A comparative study of GaInP/GaAs heterojunction bipolartransistors grown by CBE using TBA/TBP andAsH3/PH3 sources

GaInP/GaAs heterojunction bipolar transistors (HBT's) have been fabricated on epitaxial layers grown by chemical beam epitaxy (CBE) using an all metalorganic approach. Reduced toxicity tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) were used for group V sources. DC results showed good base and collector current ideality factors of 1.23 and 1.05 respectively. The maximum DC current of 50 was obtained. A comparison of these results with HBT characteristics obtained using AsH ₃/PH₃ or TBA/PH₃ demonstrates the feasibility of replacing the toxic AsH₃ and PH₃ by less toxic TBA and TBP sources in the growth of GaInP/GaAs HBT's     

Growth of P-type Znse by metalorganic molecular beam epitaxy using metal Zn and dimethylselenide

This paper describes metalorganic molecular beam epitaxy (MOMBE) of p-type ZnSe using metal zinc, pre-cracked metalorganic dimethylselenide, and microwave-excited nitrogen plasma as sources. Optical, structural, and electrical properties of the p-type ZnSe layers have been investigated. At present, maximum net acceptor concentration N_a-N_d is 3 x 10¹⁷ cm^-3 without any post-growth annealing. This is the highest acceptor concentration ever reported for MOMBEgrown p-type ZnSe doped with nitrogen plasma, but photoluminescence and deep level transient spectroscopy suggest that acceptors are highly compensated and the reduction of compensating defects is a key to further increase the acceptor concentration.     

Thermal stability of group 13 metalorganic MOVPE and CBE precursors

The thermal stabilities of a range of group 13 metalorganic compounds previously used as precursors in metalorganic vapour phase epitaxy (MOVPE) or chemical beam epitaxy (CBE) have been investigated using differential scanning calorimetry (DSC). For the trialkyl compounds R₃M the thermal stability decreases in the order M≡Al>Ga>In and R≡Me>Et>ⁱPr>^tBu and the formation of adducts R₃ML (L≡OR₂, NR₃, etc.) leads to an increase in thermal stability. Dialkylaluminium hydride compounds (e.g. Me₂AlH) gave the largest energy release. © 1997 John Wiley & Sons, Ltd.     

Fabrication of GaAs quantum wire structure using metal organic molecular beam epitaxy

GaAs quantum wires (100*20 nm/sup 2/) buried in AlAs layers have been successfully fabricated using metal organic molecular beam epitaxy (MOMBE) for the first time. The underlying growth mechanism is that, under appropriate As/sub 4/ pressure in MOMBE, GaAs preferentially grows only on the sidewalls of the patterned     

Growth of ultrahigh carbon-doped InGaAs and its application toInP/InGaAs(C) HBTs

Growth of ultrahigh carbon-doped p-type InGaAs lattice matched to InP by chemical beam epitaxy (CBE) using carbon tetrabromide (CBr₄ ) as a doping source was investigated. Effects of growth temperature, group V supply pressure, and CBr₄ supply pressure on growth rate, composition, mobility, and hole concentration of carbon-doped InGaAs were studied. Ultrahigh net hole concentration and room-temperature mobility of 2 × 10²⁰/cm³ and 33 cm²/V·sec, respectively, were achieved. Mobility of the ultrahigh carbon-doped InGaAs using CBr₄ compared favorably to those of CBE grown carbon-doped InGaAs using carbon tetrachloride (CCl₄) and molecular beam epitaxy grown beryllium (Be)-doped InGaAs grown at low temperature. The highly carbon-doped InGaAs layers grown by CBE using CBr₄ as a doping source showed a negligible hydrogen passivation effect and were used for the growth of high-performance, highly carbon-doped base InP/InGaAs heterojunction bipolar transistor epitaxial layer structures     

Reflectance and photoreflectance for in-situ monitoring of the molecular beam epitaxial growth of CdTe and Hg-based materials

Epitaxial growth of Hg-based semiconductors by molecular beam epitaxy (MBE) and metalorganic MBE (MOMBE) has progressed sufficiently to shift emphasis to the control of factors limiting the yield of both materials and devices. This paper reports on anex-situ study to evaluate the suitability of reflectance and photoreflectance (PR) asin-situ characterization techniques for the growth of CdTe and HgCdTe. Photoreflectance yields information about CdTe layers, with largest utility for doped and multi-layer structures. However, caution must be taken in interpretation of the spectra since the near-bandedge PR spectra consists of multiple transitions and the E₁ transition energy is very sensitive to the sample history. Photoreflectance appears to be of limited utility for HgCdTe single layer growth with x<0.4. However, reflectance measurements of the E₁ peak can be used to determine composition in HgCdTe single layers with an accuracy Δx = ±0.01, which can be useful for growth control. A tight binding model was used to calculate the E₁ peak energy as a function of bandgap for HgCdTe and HgTe/CdTe superlattices. Comparisons are made with experimental observations. Surface interdiffusion in HgTe-CdTe superlattices was probed using reflectance measurements.     

High-speed InP/InGaAs heterojunction bipolar transistors

Very-high-performance common-emitter InP/InGaAs single heterojunction bipolar transistors (HBTs) grown by metalorganic molecular beam epitaxy (MOMBE) are reported. They exhibit a maximum oscillation frequency (f_T) of 180 GHz at a current density of 1×10⁵ A/cm². this corresponds to an (R_BC_BC)_eff=f _T/(8πf²_max) delay time of 0.12 ps, which is the smallest value every reported for common-emitter InP/InGaAs HBTs. The devices have 11 μm² total emitter area and exhibit current gain values up to 100 at zero base-collector bias voltage. The breakdown voltage of these devices is high with measured BV_CEO and BV_CEO of 8 and 17 V, respectively     

'High frequency' quasiplanar GaInP/GaAs HBT with CBE selective collector contact regrowth

Quasiplanar GaInP/GaAs heterojunction bipolar transistors (HBTs) with selective regrowth of the collector contact are reported. Such devices have a planar surface topology which should allow large scale integration. The multilayer HBT structure and the selective regrown collector contact are realised by chemical beam epitaxy (CBE). Cutoff frequency and maximum oscillation frequency of 30 and 25 GHz respectively, have been obtained for devices with 2*15 mu m/sup 2/ emitter-base junction area.<>     

Growth characteristics of hydride-free chemical beam epitaxy and application to GaInP/GaAs heterojunction bipolar transistors

We report on the complete characterization of a hydride- and hydrogen-free chemical beam epitaxy (CBE) process for the realization of GaAs/GaInP heterojunction bipolar transistors. Alternative group V sources tertiarybutylarsine, tertiarybutylphosphine, and trisdimethylaminoarsenic are used instead of traditionally employed AsH₃ and PH₃. A very high degree of reproducibility of growth parameters (fluxes, substrate temperature, doping levels) is demonstrated. Total defect densities lower than 10 def/cm² are routinely obtained. Large-area GaInP/GaAs heterojunction bipolar transistors (HBTs) show a high current gain of 225 for base sheet resistance of 400 ohm/sq. The devices also exhibit excellent high-frequency characteristics. A cut-off frequency of 48 GHz and a maximum oscillation frequency of 60 GHz have been obtained. These results demonstrate the high potential capability of CBE for high-throughput GaInP/GaAs HBT production.