Intrinsic N-Type Modulation Doping in Inp-Based Heterostructures

We propose and demonstrate a new doping approach, i.e. intrinsic doping, for n-type modulation doping in InP-based heterostructures. Instead of the conventional method of n-type doping by shallow donor impurities, grown-in intrinsic defects are utilized to provide the required doping without external doping sources. The success of this approach is clearly demonstrated by our results from InGaAs/InP heterostructures, where the required n-type doping in the InP barriers is provided by Pin antisites, preferably introduced during off-stoichiometric growth of InP at low temperatures (LT-InP) by gas source molecular beam epitaxy. A twodimensional electron gas (2DEG) is shown to be formed near the InGaAs/InP heterointerface as a result of electron transfer from the LT-InP to the InGaAs active layer, from studies of Shubnikov-de Haas oscillations and photoluminescence. The concentration of the 2DEG is determined to be as high as 1.15×1012 cm−2, where two subbands of the 2DEG are readily occupied.

Current Transport in Cryogenic Processed Metal/InP and GaAs Interfaces

ABSTRACTSchottky contacts to n type InP and GaAs have been made by deposition on substrates cooled to low temperature (LT=77K) in a vacuum close to 10-7 Torr.The Schottky barrier height, ФB, was found to be as high as 0.96eV with Pd/InP and 0.95eV for Au/GaAs. This indicated a significant increase in ФB compared with the room temperature (RT=300K) deposition. For diodes fabricated at room temperature, the reverse saturation current density, JO, decreased sharply with decrease in measuring temperature. For the RT InP diodes, the conduction mechanism was controlled by thermionic emission (TE). For the LT InP diodes, the value of JO was about six orders smaller than for the RT diode at the same temperature. As testing temperature decreased, the barrier height was increased from 0.96 to 1.15eV, with a temperature coefficient of -3.2 x 10-4 eV/K. The forward transport mechanism was controlled by thermionic field emission (TFE). For the GaAs diodes, thermionic emission (TE) dominated in the current transport at room temperature for both RT and LT diodes. At low testing temperature, RT diodes exhibited an excess current component at low forward bias.

CBED study of low-temperature InP grown by gas source MBE

In our previous work on MBE grown low temperature (LT) InP, attempts had been made to understand the relationships between the structural and electrical properties of this material system. Electrical measurements had established an enhancement of the resistivity of the phosphorus-rich LT InP layers with annealing under a P2 flux, which was directly correlated with the presence of second-phase particles. Further investigations, however, have revealed the presence of two fundamentally different types of precipitates. The first type are the surface particles, essentially an artefact of argon ion milling and containing mostly pure indium. The second type and the one more important to the study are the dense precipitates in the bulk of the annealed layers. These are phosphorus-rich and are believed to contribute to the improvement in the resistivity of the material.The observation of metallic indium islands solely in the annealed LT layers warranted further study in order to better understand the exact reasons for their formation.

HREM of low-temperature InP grown by gas source MBE

In recent times, following the application of MBE GaAs grown at low temperatures as an electrical buffer layer in field effect transistors, there has been a focus of attention on other III-V materials grown at low temperatures. This lead to speculation on the possibility of applications of low temperature (LT) InP in electronic and photonic devices resulting in a need to correlate the structural properties of this material with the electrical and optical measurements. The current endeavour is directed toward studying the structure and the morphology of LT InP synthesized under varying growth conditions in order that a correlation with properties like conductivity and photoluminescence can be effected.In this present study, InP grown at low temperatures by gas source MBE using for sources solid indium and P2 has been characterized by TEM. Samples were prepared by mechanical grinding, dimpling and low-angle argon ion-milling. The low-angle technique was employed because it greatly mitigates the formation of indium islands during the milling of InP samples with Ar+ ions. Observations were made on an ISI 002B electron microscope, operating at 200 kV.

Low-Temperature Growth and Characterization of InP Grown by Gas-Source Molecular-Beam Epitaxy

ABSTRACTLow-temperature (LT) growth of InP by gas-source molecular-beam epitaxy has been studied. Contrary to GaAs, InP grown at low temperature (from 200°C to 410°C) shows ntype, low-resistivity properties. The electron concentration changes dramatically with growth temperature. A model of P antisite defects formed during LT growth was used to explain this experimental result. Ex-situ annealing can increase the resistivity, but only by a factor of about 6. Heavily Be-doped LT InP also shows n-type property. We believe this is the first report of an extremely high concentration of donors formed in LT InP and n-type doping by Be in III–V compounds.