L. L. Taylor

InGaAs‐InP multiple quantum wells grown by atmospheric pressure metalorganic chemical vapor deposition

The optical and structural properties of multiple quantum wells of InGaAs‐InP grown by atmospheric pressure metalorganic chemical vapor deposition are reported. Room‐temperature excitons are resolved for well widths from 50 to 200 A. Below 50 K, exciton linewidths, in absorption, of less than 10 meV are obtained. Absorbances for allowed valence to conduction subband transitions are found to be independent of well width, as expected in the two‐dimensional limit. A lower bound for the conduction‐band discontinuity of 235±20 meV is obtained.

Identification of donors in vapor grown indium phosphide

We report well resolved substructure in the ‘‘two electron’’ satellite (TES) near band‐gap photoluminescence (PL) of excitons bound to shallow donors in InP, observable in high magnetic fields above ∼3 T. This substructure arises from differences in the central cell corrections to the binding energies of different donor species, resolved here for the first time in PL spectra for InP. Six different donor species are differentiated in undoped vapor phase epitaxial (VPE) layers. The two most persistent contaminants are identified with S and Si from back‐doped crystals which yield useful data for uncompensated donor concentrations up to ∼5×1015 cm−3 at ∼9.5 T. The most important donor contaminant in refined halide transport VPE InP is S, but Si is dominant in layers grown with metalorganic sources of In. The TES identifications are supported by similar substructure with appropriately reduced splittings in the ionized donor BE PL. A profile of the Si/S donor concentration ratio as a function of layer thickness...

Transport properties and persistent photoconductivity in InP/In0.53Ga0.47As modulation‐doped heterojunctions

This paper reports a study of the electrical properties of a systematic series of InP/In0.53Ga0.47As modulation‐doped heterostructures grown by metalorganic chemical vapor deposition. Both Hall‐effect and Shubnikov–de Haas measurements are used to obtain consistent values for carrier densities and mobilities. The heterostructures are shown to display a persistent photoconductive effect at low temperatures (<80 K) which results in changes in both the carrier density and the mobility. The variation of mobility with carrier density is analyzed to show that alloy disorder and background charged impurity scattering are the dominant scattering mechanisms. Excitation across the InP band gap is shown to be necessary for the persistent photoconductivity. We propose a mechanism for this effect in which electron hole pairs created by illumination are separated by electric fields built into the heterojunction with the holes subsequently being trapped in the InP substrate.

Identification of germanium and tin donors in InP

Central cell structure due to germanium and tin donors in InP is identified in carefully back‐doped vapor phase epitaxial material. Both near band edge photoluminescence and far infrared photoconductivity in high magnetic fields are employed to resolve spectral features arising from different donor species. Relative to the likely effective mass donor binding energy of 5.46 meV, the Ge and Sn chemical shifts are deduced to be 0.30 and 0.21 meV, respectively.

A study of layer composition of InGaAs/InP multiquantum wells grown by metalorganic chemical vapor deposition using double‐crystal x‐ray diffraction theory and experiment

InGaAs/InP multiquantum wells grown by metalorganic chemical vapor deposition have been studied by fitting computer simulated theoretical double‐crystal x‐ray rocking curves to experimental data. It is shown that the technique can identify the carry over of As into the InP barriers and the concentration and distribution of As are determined. The highest concentration of As observed was 21%, which was confined to the first 50 A of the barrier and fell to 2% towards the following interface. Both the maximum and minimum concentration of As was found to decrease as a function of the pause time between growth of the InGaAs quantum well and the InP barrier layers. These observations were confirmed by secondary ion mass spectrometry (SIMS) and other experimental data on the same material is shown to support the results.

Transport and persistent photoconductivity in InGaAs/InP single quantum wells

Hall effect and Shubnikov–de Haas data are presented for single 100 A InGaAs/InP quantum wells grown by atmospheric pressure metalorganic chemical vapor deposition. Both modulation doped and nominally undoped structures are studied. Measurements are made on the latter structures by using the low‐temperature persistent photoconductivity to put carriers into the quantum well. Mobilities as high as 95 000 cm2/V s have been achieved at carrier densities of 9×1011 cm−2. The persistent photoconductivity effect is also used to study the dependence of mobility on carrier density and the data are analyzed in terms of ionized impurity and alloy disorder scattering.

X-ray microanalysis of InGaAs/InP multilayer structures grown by metalorganic chemical vapor deposition

X‐ray microanalysis in a scanning transmission electron microscope can be employed to determine concentration profiles with a spatial resolution of ≲2 nm across layer interfaces in III‐V compound semiconductor multilayer structures. Here we describe its application to the InGaAs/InP multilayer system grown by metalorganic chemical vapor deposition at atmospheric pressure. The results show that even when the material is structurally perfect, there can be a significant As and Ga content beyond the boundaries of the InGaAs layers. Furthermore, the composition profiles can show a marked asymmetry relating to the growth direction. The results are consistent with previous imaging observations but provide quantitative information with high spatial resolution on individual element distributions. This combination of analytical attributes is not available using any other assessment technique.

Photoluminescence and magneto-transport of wide InGaAsInP modulation doped quantum wells

Abstract A photoluminescence (PL) study of 700A wide modulation doped InGaAsInP quantum wells in magnetic fields up to 10 Tesla, is reported. PL from the lowest electron sub-bands, localised in the space charge potentials at the two sides of the QW, and from higher delocalised sub-bands extending across the whole width of the QW, is observed. The performance of simultaneous Quantum Hall Effect (QHE), Shubnikov-de-Haas and PL measurements is found to be crucial to obtain a reliable understanding of the behaviour of the PL spectra in magnetic field. In particular the QHE provides direct information on the number of filled sub-bands and Landau levels in a complicated system of total carrier density ∼1012 cm−2, containing several populated electronic sub-bands.

Magneto-optical studies of GainAsInP quantum wells

Abstract The optical properties of GainAsInP quantum wells are studied in magnetic fields of up to 16T. A comparison of the absorption and photoluminescence spectra of a series of multiple quantum wells provides evidence that the photoluminescence occurs from excitons in which the hole is localised. This localisation is shown to be present in a highly doped sample with a sheet carrier density of ∼10 12 cm −2 , indicating that the localisation is not screened out by high free carrier densities. A theoretical fit to measured Landau level transitions in a 100A multiple quantum well allows values for the carrier masses, electron non-parabolicity and exciton binding energy to be determined.

Luminescence of narrow RIE etched In1−xGaxAs/InP and GaAs/Ga1−xAlxAs quantum wires

Abstract We present low temperature optical data obtained on narrow quantum wires, fabricated with reactive ion etching and MOCVD overgrowth, in both In1−xGaxAs/InP and GaAs/Ga1−xAlxAs systems. One-dimensional quantum confinement effects are observed in both cases for the lowest lateral sizes (Lx), in which carrier lifetimes remain of the order of one nanosecond. For In1−xGaxAs/InP wires (Lx down to 15 nm, quantum shifts of the photoluminescence peak (up to 30 meV) are observed. For GaAs/Ga1−xAlxAs wires (Lx down to 20 nm). We present photoluminescence excitation spectra showing additional lateral confinement effects, concerning mainly the polarization of the observed transitions.