Surface passivation of lnP/ln0.53Ga0.47As heterojunction bipolar transistors for opto-electronic integration

We report for the first time, a surface passivation technique for InP/In_0.53Ga_0.47As heterojunction bipolar transistors that is suitable for optoelectronic integrated circuits. The combination of buffered hydrofluoric acid with high temperature annealing of the surface causes significant increase of the gain at low input currents. Using this technique, transistors were integrated with photodetectors and other optoelectronic devices and had current gains as high as 400 even at nanoampere base currents.     

Interface structure in arsenide/phosphide heterostructun grown by gas-source MBE and low-pressure MOVPE

We have used cross-sectional scanning tunneling microscopy (STM) to study interface structure in arsenide/phosphide heterostructures grown by gas-source molecular beam epitaxy (GSMBE) and by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). High-resolution images of GSMBE samples consisting of GaAs interrupted at 200Å intervals with a 40 s P₂ flux reveal substantial, growth-temperature-dependent incorporation of phosphorus with nanometer-scale lateral variations in interface structure. STM images of InGaAs/InP multiple quantum well structures grown by LP-MOVPE show evidence of interface asymmetry and extensive atomic cross-incorporation at the interfaces. Data obtained by STM have been corroborated by high-resolution x-ray diffraction and reflection high-energy electron diffraction. Together, these studies provide direct information about nanometer-scale grading and lateral nonuniformity of arsenide/phosphide interfaces that can occur under these growth conditions.     

Chemical-bonding structure of InP surface in MOVPE studied by surface photo-absorption

Using surface photo-absorption spectra, we established a phase diagram of the surface chemical-bonding structure for the P-stabilized surface in InP metalorganic vapor phase epitaxy as a function of substrate temperature and PH₃ partial pressure. At 550°C and PH₃ partial pressures of 10 and 30 Pa, the surface is (2 × 4)-like consisting of P dimers having a bond axis parallel to [110]. As the substrate temperature decreases and the PH₃ partial pressure increases, amorphous P species start to adsorb excessively on (2×4)-like P dimer surface. A c(4 × 4)-like surface was not observed. From InP growth experiments for each P surface phase, we found that, to obtain high-quality InP epitaxial layers, excess P adsorption should be suppressed by minimizing the formation of native defects.     

MOVPE growth of InPSb/InAs heterostructures for mid-infrared emitters

We investigated the growth of InPSb on GaSb or InAs by low pressure (20 mbar) metalorganic vapor phase epitaxy (MOVPE). Trimethylindium, triethylantimony, and phosphine were used as starting materials. High resolution x-ray diffraction, photoluminescence at 10K, Hall measurements at 300 and 77K as well as scanning electron microscopy and scanning tunneling electron microscopy investigations were carried out to verify the layer properties. Lattice-matched InPSb layers on InAs substrate grown at 520°C show mirror-like surfaces and sharp x-ray peaks. N-type doping of InP_0.69Sb_0.31 was carried out with H₂S and p-type doping was achieved with DEZn. Maximum electron concentrations of 2×10¹⁹ cm⁻³ and hole concentrations exceeding 10¹⁸ cm⁻³ were obtained after annealing in N₂ ambient. The thermal stability of InPSb was studied during annealing experiments carried out at 500°C up to 30 min. The compositional integrity of the lattice proves to be stable and the InAs/InPSb interface can be improved. Multiple quantum well structures, pn-junction diodes and the two-dimensional electron gas at the InPSb/InAs/InPSb quantum wells were investigated to demonstrate the properties of the material.     

Selective LPE-growth of ln0.53Ga0.47As on semi-insulating InP

Selective liquid phase epitaxy (SLPE) of high purity(n = 2 × 10¹⁵ cm^-3) In_0.53Ga_0.47As on SiO₂-masked (100)-InP:Fe substrates has been performed and investigated using Normarski interference contrast microscopy and SEM. The infill growth was done at low temperatures (˜ 585° C) directly into chemically (HC1:CH₃COOH:H₂O₂) etched cavities without melt-etching. Square and circular recesses of 2–3 μm depth and varying size (100-500 μm) have been used in contrast to common reported regrowth experiments in long channels. Enormously enhanced growth rates have been found within the small structures. Orientation dependent growth effects are described. The realization of selectively grown areas with flat surface morphology has been achieved which is important for optoelectronic integration. Most information contained in this paper was presented at the 27th Electronic Materials Conference, Boulder, Co., June 20, 1985.     

Metalorganic vapor phase epitaxy of InP using the novel P-source ditertiarybutyl phosphine (DitBuPH)

In this study, the use of a novel phosphorous precursor for low pressure metalorganic vapor phase epitaxy (LP-MOVPE) application has been investigated. Ditertiarybutyl phosphine ((C₄H₉)₂-P-H, DitBuPH) as substitute for the standardly used hydrid gas phosphine (PH₃) promises apart from strongly reduced toxicity due to the reduction of P-H bonds, an enhancement in cracking efficiency as well as a reduction in growth temperature. Layer quality has been examined by means of optical and scanning electron microscopy (SEM), temperature-dependent van der Pauw Hall as well as photoluminescence (PL) measurements. Uncompensated n-type InP-layers (1.0 x 1.5 cm^-3; 59600 cm²Vs)^-1 at 77K) are realized using DitBuPH in combination with commercial TMIn. All results are compared with those obtained by using PH₃ and commercial tertiarybutyl phosphine (TBP) as P-source, respectively.     

MOVPE growth of AlGaAs/GaInP diode lasers

GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better carrier confinement. Such structures show very high slope efficiencies and a high T₀. Maximum output powers of 7 W CW are obtained from 4 mm long devices.     

The origin of hillocks in (Hg, Cd)Te grown by MOVPE

Dimethylcadmium, a precursor for the metalorganic vapor phase epitaxy of mercury cadmium telluride, has been shown to react with gallium arsenide to form trimethylarsine and dimethylarsine. An analogous reaction occurs between di-iso-propyltelluride and gallium arsenide to form iso-propylarsine and di-iso-propylarsine. It is proposed that if these reactions remove sufficient arsenic from a gallium arsenide substrate, metallic droplets will form on the wafer surface thereby creating the nucleation sites for hillocks. Analogous reactions have been observed between the precursors and a range of other substrates which can in turn be used to explain the origin of hillocks in epitaxial layers grown onto these materials.     

GaAs microlens arrays grown by shadow masked MOVPE

This paper describes the fabrication of high quality GaAs microlenses and microlens arrays using shadow masked metalorganic vapor phase epitaxial (MOVPE) growth (SMMG). Microlenses with apertures as small as 30 μm were fabricated and focal lengths down to 40 μm were measured. The smaller lenses closely fit the theoretical behavior of ideal spherical lenses while larger lenses (focal length >80 μm) showed a more complex physical shape and could not be modeled as spherical. This deviation from a spherical shape is expected from simulation of SMMG. The full width at half maximum of the beam waist was <2 μm for all sizes of microlens indicating that these lenses are compatible with coupling to single mode fibers.     

New mechanisms in photo-assisted MOVPE of II-VI semiconductors

The first detailed comparison has been made of the metalorganic vapor phase epitaxy growth rates of CdTe, ZnTe, and ZnSe, measured in situ with laser reflectometry. The comparison also includes the photo-assisted growth with visible radiation from an argon ion laser. Using a standard Group II precursor (DMCd or DMZn.TEN) partial pressure of 1.5 × 10⁻⁴ atm, VI/II ratio of 1 and DIPM (M = Te, Se) the maximum growth rates are in the region of 10 to 15 AU/ s. Decrease in growth rates of ZnTe at higher temperatures or higher laser powers have been attributed to the desorption from the substrate of unreacted Te precursor. The behavior of DTBSe is quite different from DIPSe for both pyrolytic and photo-assisted growth. The maximum growth rate is around 1 AU/ s with very little photo-enhancement, except at 300°C. Secondary ion mass spectroscopy analysis of hydrogen concentration in the ZnSe layers shows high concentrations, up to 5.9 × 10¹⁹ atoms cm⁻³ for DTBSe grown ZnSe under pyrolytic conditions. These results show that the growth kinetics play an important part in the incorporation of hydrogen and passivation of acceptor doped material.     

MOVPE production reactors for high temperature electronics

For the fabrication of epitaxial films of silicon carbide or the Group III nitrides, high growth temperatures (up to 1700°C) and fast heating and cooling of the growth environment have been found to be necessary. A range of production systems meeting these requirements has been designed with different loading capacities. In this paper, we present results from various machines showing the high quality and excellent homogeneity obtainable for 3C-SiC on Si and on 6H-SiC, as well as GaN on sapphire.     

Metalorganic vapor phase epitaxial growth and structural characterization of GaAs/InP heterostructures

Highly mismatched GaAs epitaxial layers with thickness ranging from 15 nm to 7 μm have been grown on InP substrates by atomospheric pressure metalorganic vapor phase epitaxy. Layers thinner than 30 nm exhibited 3-D growth mechanism; in the thicker layers, the islands coalesced and then the growth followed the layer by layer mechanism. The elastic strain and the extended defects have been studied by high resolution x-ray diffraction and transmission electron microscopy, respectively. The common observation of planar defects, misfit, and threading dislocations in the layers has been confirmed. The results on the elastic strain release have been discussed on the basis of the equilibrium theory.     

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

We have demonstrated that a self-organization phenomenon occurs in strained InGaAs system on InP (311) substrates grown by metalorganic vapor phase epitaxy. This suggests that a similar formation process of nanocrystals exists not only on the GaAs (311)B substrate but also on the InP (311)B substrate. However, the ordering and the size homogeneity of the self-organized nanocrystals are slightly worse than those of the InGaAs/AlGaAs system on the GaAs (311)B substrate. The tensilely strained condition of a InGaAs/InP system with growth interruption in a PH₃ atmosphere reveals a surface morphology with nanocrystals even on the InP (100) substrate. It was found that strain energy and high growth temperature are important factors for self-organization on III-V compound semiconductors. Preliminary results indicate that the self-organized nanostructures in strained InGaAs/InP systems on InP substrates exhibit room temperature photoluminescent emissions at a wavelength of around 1.3 p.m.     

A comparison of ethyl iodide and hydrogen chloride for doping ZnSe grown by photoassisted MOVPE

We have conducted a study of the electrical and photoluminescence properties of ZnSe films grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) (250 Torr, 400°C) with ethyl iodide and hydrogen chloride as n-type dopant sources. A higher peak electron concentration and a lower minimum resistivity were observed using hydrogen chloride (5.4 × 10¹⁸ cm⁻³, and .0070 ohm-cm, respectively), as opposed to ethyl iodide (1.55 × 10¹⁷ cm ⁻³, and 0.067 ohm-cm, respectively). We show that the higher electron concentrations observed in the chlorine doped layers are due to a higher incorporation of chlorine atoms than that of iodine atoms, and that this may be a result of the different tetrahedral misfit factors for these atoms. Our photoluminescence and 77K Hall effect data support this conclusion. Growth rate depression was observed to be more severe for iodine doped layers than for chlorine doped layers. Thus, it appears that hydrogen chloride is a superior dopant source for low-temperature photoassisted MOVPE ZnSe growth of n-type layers for blue-green laser diodes in the pressure-temperature regime investigated.     

InAIGaAs selective MOVPE growth with bandgap energy shift

We studied the bandgap energy shift by varying the SiO₂ mask width in selective MOVPE growth of InAIGaAs with almost no polycrystals on the masks. We found that the photoluminescence (PL) peak shifts toward the longer wavelength with wider mask width and narrower mesa width, where the In content is enhanced, and observed a maximum PL peak wavelength shift of 170 nm.     

Optical and crystallographic properties of high perfection InP grown on Si(111)

The growth of InP by low-pressure metalorganic chemical vapor deposition on vicinal Si(111), misoriented 3° toward [1-10], is reported. Antiphase domain-free InP is obtained without any preannealing of the Si substrate. Crystallographic, optical, and electrical properties of the layers are significantly improved as compared to the best reported InP grown on Si(001). The high structural perfection is demonstrated by a full width at half maximum (FWHM) of 121 arcs for the (111) Bragg reflex of InP (thickness = 3.4 μm) as obtained by double crystal x-ray diffraction. The low-temperature photoluminescence (PL) efficiency is 70% of that of homoepitaxially grown InP layers. The FWHM of the near-gap PL peak is only 2.7 meV as compared to 4.5 meV of the best material grown on Si(001). For the first time, InP:Fe layers with semi-insulating characteristics (ρ > 3 × 10⁷ Ω-cm) have been grown by compensating the low residual background doping using ferrocene. Semi-insulating layers are prerequisite for any device application at ultrahigh frequencies.     

Large scale production of indium antimonide film for position sensors in automobile engines

We use low pressure MOVPE to grow indium antimonide films on groups of eight 3 inch GaAs wafers per run. The films are used for the production of magnetoresistive position sensors for the car industry. To meet the narrow specifications for automotive components, the standard deviation of the sheet resistivity, and the thickness of the films have been reduced below 1.5%. This uniformity is the result of an optimization process encompassing the determination of the best susceptor temperature and the optimum flow. The gas velocity was found to have a large impact on the uniformity of the layers. Rotation of the wafers and the use of an optimum gas velocity results in extremely uniform layers.     

Thermal stability of Al0.48In0.52As/Ga0.47In0.53As/InP heterostructure and its improvement by phosphidization

A drastic decrease in the sheet carrier concentration of modulation-doped Al_0.48In_0.52As/Ga_0.47In_0.53As/InP heterostructures has been observed after O₂ plasma treatment followed by thermal treatment up to 350°C. The decrease in sheet carrier concentration, which is speculated to be caused by both plasma damage and impurities penetrating from the surface of the epilayer, can be suppressed substantially by using PH₃ plasma treatment prior to the O₂ plasma and thermal treatments.     

MOVPE growth of strained InGaAs/lnAIAs MQWs for a polarization-insensitive electroabsorption modulator

Metalorganic vapor phase epitaxial growth of a strained InGaAs/lnAIAs multiquantum well (MQW) structure was carried out for optical electroabsorption modulators. A high-quality MQW layer can be grown by introducing compressive strain into InAlAs barrier layers against tensile-strained well layers. We have also demonstrated strained InGaAs/lnAIAs MQW electroabsorption modulators with polarization insensitivity by using these layers and have obtained a highquality modulator with a low driving voltage of 1.7 V and a wide 3-dB bandwidth of over 20 GHz.     

Growth kinetics of GaSb by metalorganic vapor phase epitaxy

The growth rates of GaSb by metalorganic vapor phase epitaxy were studied as functions of growth temperatures and partial pressures of precursors. A Langmuir-Hinshelwood model was used to explain the GaSb growth rate in the chemical reaction controlled regime. The relationship between growth kinetics and epilayer qualities was discussed and properties of GaSb were obtained.