Madhavie Edirisooriya

Dislocation filtering by AlxIn1−xSb∕AlyIn1−ySb interfaces for InSb-based devices grown on GaAs (001) substrates

Dislocation filtering by interfaces between AlxIn1−xSb and AlyIn1−ySb layers grown on a GaAs (001) substrate has been investigated. Transmission electron microscopy analysis shows that as many as 59% of threading dislocations (TDs) can be eliminated by such an interface. An interlayer sample that contains six Al0.12In0.88Sb∕Al0.24In0.76Sb interfaces has 6.0×108TDs∕cm2 at 1.6μm thickness. Compared with an Al0.12In0.88Sb epilayer without an interlayer, this TD density is a factor of ∼4 lower for the same thickness, and about the same as for a layer that is more than twice as thick. Our results suggest that AlxIn1−xSb∕AlyIn1−ySb interfaces can be used to improve the performance of any InSb-based device in which AlxIn1−xSb is used as a buffer, insulating, or barrier layer material.

Reduction of microtwin defects for high-electron-mobility InSb quantum wells

The effect of structural defects on electron mobilities has been investigated in InSb quantum wells (QWs) grown on GaAs (001) substrates. The usefulness of a ⟨116⟩-directional transmission electron microscopy analysis for microtwins (MTs) in a plan-view specimen is demonstrated. MTs and threading dislocations reduce the room-temperature (RT) electron mobility in InSb QWs. It is found that the use of 2° off-axis GaAs (001) substrates is effective in reducing MT densities in InSb QWs. The electron mobility in InSb QW at RT, 4.0×104cm2∕Vs with an electron density of 4.6×1011∕cm2, is among the highest values reported in semiconductor QWs.

Electron scattering by structural defects in InSb quantum wells: Analysis with simplified Mayadas-Shatzkes equation

The scattering of transport electrons in InSb quantum wells (QWs) caused by two types of structural defects, micro-twins (MTs) and threading dislocations (TDs), has been investigated at room temperature. The electron scattering due to a MT is explained by its energy barrier with a height of ∼0.087 eV or its reflection with a coefficient of ∼0.33. The electric charge of a TD is 1.7 × 10−10 C/m along the [001] direction which is perpendicular to the InSb QWs examined in this study, under the assumption that the electron scattering due to a TD is fully attributed to its electric field. The electron scattering efficiency of one TD line in InSb QWs is equivalent to that of MT plates with a total length of 75 nm. In the course of this study, a mathematical simplification was made for Mayadas-Shatzkes equation which is one of the most frequently used equations to analyze carrier scattering due to a planar defect.

Measurement of the Dresselhaus and Rashba Spin-Orbit Coupling Via Weak Anti-Localization in InSb Quantum Wells

Weak anti-localization has been observed in the magneto-resistance of both symmetrically and asymmetrically doped InSb/AlInSb quantum wells. We find that for both types of structures, the magnetic field corresponding to the conductance minimum is in good agreement with the dominant spin-orbit term, which is the cubic Dresselhaus and Rashba terms for symmetric and asymmetric samples, respectively.

Interband magneto-spectroscopy in InSb square and parabolic quantum wells

We measure the magneto-optical absorption due to intersubband optical transitions between conduction and valence subband Landau levels in InSb square and parabolic quantum wells. InSb has the narrowest band gap (0.24 eV at low temperature) of the III–V semiconductors leading to a small effective mass (0.014 m0) and a large g–factor (−51). As a result, the Landau level spacing is large at relatively small magnetic fields (<8 T), and one can observe spin-splitting of the Landau levels. We examine two structures: (i) a multiple-square-well structure and (ii) a structure containing multiple parabolic wells. The energies and intensities of the strongest features are well explained by a modified Pidgeon-Brown model based on an 8-band k•p model that explicitly incorporates pseudomorphic strain. The strain is essential for obtaining agreement between theory and experiment. While modeling the square well is relatively straight-forward, the parabolic well consists of 43 different layers of various thickness to appr...

Magneto‐Optical Properties of InSb Semiconductor Heterostructures

We have theoretically and experimentally studied the spin‐dependent Landau levels for electrons and holes in narrow‐gap InSb/AlInSb quantum well systems. We use the envelope function approximation for the electronic and magneto‐optical properties of InSb/AlInSb. Our model includes the conduction electrons, heavy holes, light holes and spin‐orbit split‐off holes for a total of 8 bands taking spin into account. The Pidgeon‐Brown model is generalized to include the effects of confinement in the quantum wells. In addition, strain effects are taken into account by assuming pseudomorphic growth conditions. Comparing our calculated electronic structures with experimental magneto‐absorption measurements, we obtain excellent agreement. Our results demonstrate that in addition to the major transitions, strong band mixing in the narrow gap material leads to several optical transitions which normally are forbidden.

Magnetoexcitons in Strained InSb Quantum Wells

Magneto-optical measurements of InSb quantum wells show absorption features due to transitions between Landau levels of the conduction and valance subbands. The energies and intensities of the strongest features are well explained by a modified Pidgeon-Brown model that explicitly incorporates pseudomorphic strain.

Substrate preparation effects on defect density in molecular beam epitaxial growth of CdTe on CdTe (100) and (211)B

Recent studies have demonstrated that growth of CdTe on CdTe (100) and (211)B substrates via molecular beam epitaxy (MBE) results in planar defect densities 2 and 3 orders of magnitude higher than growth on InSb (100) substrates, respectively. To understand this shortcoming, MBE growth on CdTe substrates with a variety of substrate preparation methods is studied by scanning electron microscopy, secondary ion mass spectrometry, x-ray photoelectron spectroscopy, cross sectional transmission electron microscopy, and atom probe tomography (APT). Prior to growth, carbon is shown to remain on substrate surfaces even after atomic hydrogen cleaning. APT revealed that following the growth of films, trace amounts of carbon remained at the substrate/film interface. This residual carbon may lead to structural degradation, which was determined as the main cause of higher defect density.