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Notes: This work refers basically to the detailed understanding of the natural phenomena in real tunneling metal-semiconductor contacts. A mechanism of forming extremely low-resistance nonalloyed Ti/Pt/Au ohmic contacts to a variety of III-V compound semiconductors, e.g., InGaAs, InAs, and GaAs, is presented. Epitaxial layers of either type with different doping levels ranging from 1×1019 to 2×1020 cm−3 were employed in order to determine electrical parameters that guarantee pure tunneling behavior of the contacts. Ti/Pt/Au contacts formed on p-InGaAs Zn doped to 1×1020 cm−3 and on n-InGaAs Si doped to 5×1019 cm−3 yielded a specific contact resistance of 4.8×10−8 and 4.3×10−8 Ω cm2, respectively. The same metallization scheme applied to 4×1019 cm−3 Si-doped n-InAs gave a specific contact resistance of 1.7×10−8 Ω cm2 for the as-deposited and annealed samples. An extremely low value of 2.8×10−8 Ω cm2 was evaluated for contacts on p-GaAs doped with Be to 2×1020 cm−3. The contact properties are discussed in relation to the effect of ion-beam cleaning and postdeposition annealing. Of particular concern was the cleaning of the semiconductor surface with low-energy (60 eV) Ar+ ions for 40 s prior to the metallization process. This opens also the possibility to investigate ion damage defects and trap-assisted increase of the depletion depth. The contact design was based on the concept that the detrimental influence of the ion beam on the semiconductor properties can be neutralized with a proper annealing. It has been demonstrated that even very rapid thermal processing for 1 s at elevated temperatures was sufficient to restore the stoichiometry in the As-depleted subsurface layer arising as a result of ion damage.The fabrication sequences used provide formation of intimate contacts without interfacial films and carrier compensation effects. Optimal processing conditions have been empirically established that stimulate substantially the ohmic behavior of the contacts. It was possible to achieve an absolute control over the contact formation mechanism without crucial adjustment of annealing parameters. Closer examination of the temperature dependence of the contact resistances reveals a good agreement with the theoretical approach based on the tunneling model. Metallurgical studies of the contacts confirm their unreacted, abrupt metal-semiconductor configurations if optimal annealing temperatures are used. Experimental evidence manifests a definite relationship between electrical properties and interfacial compositional modifications affected by different forming conditions. The trend for structural changes occuring at annealing temperatures above the optimal ones was found to be in correlation with the chemical reactivity of III-V compounds. The observed thermal stability of the contacts can be fully explained in this way. In contrast to chemical precleaning the controllable elimination of interface inhomogeneities during ion etching results in contacts with improved homogeneity and uniformity. The demonstrated universality and reliability make the fabrication technique suitable to meet specific needs of modern semiconductor devices.

Notes: Extremely low resistance nonalloyed Ti/Pt/Au contacts have been formed to n-InGaAs, p-InGaAs, and n-InAs/InGaAs layers with doping concentrations ranging from 1 to 5×1019 cm−3 for n-type and from 2 to 1×1020 cm−3 for p-type material. The comparative studies reveal specific contact resistances as low as 1.7×10−8 Ω cm2 for the n-InAs/InGaAs system, while the best values obtained for n-InGaAs and p-InGaAs are 4.3 and 4.8×10−8 Ω cm2, respectively. The electrical behavior of the contacts is discussed in relation to the effect of ion beam cleaning and post-deposition annealing. The use of low energy (60 eV) Ar+ bombardment provides atomically clean, contamination free surfaces. Very rapid thermal processing at 400 °C for 1 s was successfully employed in order to restore the original properties of the subsurface layer disordered during ion bombardment. This fabrication sequence ensures formation of intimate contacts without interfacial films and carrier compensation effects. The variation of the specific contact resistance with the reciprocal square root of the carrier concentration indicates that tunneling is the dominant mechanism of current flow through the metal-semiconductor junction. The tunneling origin of the contact characteristics has also been elucidated from the temperature dependence of the contact resistance.

Notes: The structural and optical properties of molecular beam epitaxy-grown In0.52Ga0.18Al0.30As layers (E300 Kg(approximately-equal-to)1.18 eV), suitable for waveguide applications, have been studied by means of high-resolution x-ray diffraction, absorption, photoluminescence, photoreflectance, and high-excitation intensity photoluminescence spectroscopy. The combination of these techniques allowed us to study the free-exciton states, the impurity related transitions, and the formation of a dense electron-hole plasma.

Notes: Low-temperature photoluminescence (PL) and Raman measurements were performed on AlInAs grown lattice matched to InP by molecular beam epitaxy at reduced growth temperature (Ts). The PL of layers grown at Ts above 500 °C is dominated by excitonic emission, whereas for lower Ts donor-acceptor related transitions prevail. Below a critical Ts of 450 °C a marked shift towards lower emission energies with a maximum shift near 400 °C is observed that is attributed to a modified band edge due to clustering. Comparable trends are detected by Raman spectroscopy. The observed reduction of the separation of the InAs- and AlAs-like longitudinal optical phonon modes (LOInAs and LOAlAs) demonstrates local internal strain to be present as a result of clustering. This effect reaches a maximum for Ts at 400 °C. A shift of the LOInAs solely accounts for this behavior. In addition strong asymmetric broadening of the LOAlAs-phonon line observed on low Ts material indicates an increasing reduction of the correlation length and suggests the structural disorder to be correlated with the AlAs sublattice. Taking into account the pressure dependence of the AlInAs energy gap and the frequency shift of the LOInAs phonon, the local internal strain equivalent pressure was calculated from the PL and Raman results, respectively, giving similar values of up to 5 kbar for material grown at 400 °C.

Notes: Undoped Ga0.47In0.53As layers were grown by molecular beam epitaxy lattice matched to InP at substrate temperatures, Ts, in the range from 100 to 600 °C. X-ray diffraction indicated a widening of the vertical lattice parameter and a simultaneous increase of the arsenic content at low growth temperature. The epitaxial layers were single-crystalline down to Ts=125 °C. The room-temperature residual carrier concentrations and the related mobilities for layers grown below 350 °C are strongly affected by Ts, whereas at 77 K an influence of Ts on these parameters is already visible at 450 °C. At the very low growth temperatures the epitaxial layers show highly conductive behavior attributed to defect induced ionized deep centers.

Notes: High frequency modulation of gain-coupled (GC) and index-coupled (IC) InGaAs/InGaAlAs distributed feedback (DFB) lasers is investigated. Laser dynamics of conventionally fabricated IC DFB lasers are compared with GC DFB lasers realized by the new technology of masked implantation enhanced intermixing. Band structure dependence of the modulation response at low temperature (T=2K) is analyzed by detuning the emission energy of the DFB lasers with respect to the gain maximum using different grating periods. Pulse widths decreasing from 53 ps down to 4.5 ps with increasing emission energy demonstrate the capability of both coupling types. The experimental results are in excellent agreement with a theory without any fit parameter based on laser rate equations. © 1995 American Institute of Physics.

Notes: Long wavelength 1.3 μm gain coupled distributed feedback (GC-DFB) lasers were realized by masked implantation enhanced intermixing. On the basis of this full planar technology GC-DFB lasers with first and second order gratings were fabricated in the InGaAs/InGaAlAs system. The lasers show clear GC-DFB laser emission with a single mode yield of 69% and remain single mode up to several times laser threshold. The results are in good agreement with the theoretical description of our gain coupled lasers by optical matrix theory. © 1994 American Institute of Physics.

Notes: Removal of native oxide from Al0.24Ga0.24In0.52As layers grown lattice-matched onto InP substrates is successfully achieved by an in situ hydrogen radical treatment prior to molecular beam epitaxy (MBE) overgrowth. Cleaning conditions using moderate substrate temperatures not necessitating a surface stabilizing arsenic flux were elaborated, which ensured complete oxide removal without deterioration of the underlying AlGaInAs material. The surface quality as assessed by high energy electron diffraction, and the quality of epitaxial layers deposited onto this surface were found to be at least equivalent to that achieved with epitaxial growth directly on InP substrates, indicating the achievement of thorough oxide removal, low residual contamination levels, and a surface smoothness adequate for MBE regrowth.

Notes: Iron doping of InP and GaInAsP(λg=1.05 μm) layers grown by metalorganic molecular beam epitaxy was studied using elemental source material in combination with a conventional effusion cell. This study was aimed at the creation of semi-insulating optical waveguides under growth conditions compatible with selective area growth. Secondary ion mass spectroscopy measurements revealed a reproducible and homogeneous incorporation behavior of the iron dopant in the materials investigated. Resistivities in excess of 109 Ω cm were obtained for both compositions at medium doping levels. GaInAsP/InP waveguide structures grown at 485 °C—the minimum temperature necessary for selective deposition—exhibited averaged resistivities of 5×107 Ω cm in combination with optical losses of 2.5±0.5 dB/cm. © 1998 American Institute of Physics.