L. H. Peng

Electron intersubband transitions to 0.8 eV (1.55 μm) in InGaAs/AlAs single quantum wells

We report a polarization‐resolved infrared absorption study of the quantum‐well‐width dependence of the electron intersubband transitions in strained InGaAs/AlAs single quantum wells (SQWs) 3, 4, and 5 monolayers (ML) in width. An intersubband transition energy as high as 0.8 eV (i.e., a wavelength as short as 1.55 μm) is observed with transverse magnetic field polarization for a 3‐ML‐thick InGaAs SQW. This is the highest quantum‐well intersubband transition energy ever reported in any materials system.

Transverse electric and transverse magnetic polarization active intersubband transitions in narrow InGaAs quantum wells

Polarization‐resolved infrared spectroscopy has been used to demonstrate the existence of transverse electric (TE) and transverse magnetic (TM) active intersubband transitions in lattice‐matched, unstrained In0.53Ga0.47As/In0.52Al0.48As and strained In0.7Ga0.3As/AlAs quantum wells grown by molecular beam epitaxy on Fe‐doped semi‐insulating InP (001) substrates. It is shown that a previously reported intersubband absorption peak at 0.3 eV in a 4.0‐nm wide, lattice‐matched InGaAs/InAlAs quantum well can be resolved into two peaks active for TE and TM polarizations, respectively, with a 10 meV splitting between them. Bound to quasibound state transition at 0.59 eV (2.1 μm) for a narrow, 2.8‐nm‐wide InGaAs quantum well has also been observed. Group symmetry analyses considering D2d symmetry, tetragonal perturbation of local crystal and strain deformation potential, and interface roughness of the ternary quantum‐well structure is proposed to explain the polarization selection rules, and the Stark splitting in ...

Observation of 1.798 μm intersubband transition in InGaAs/AlAs pseudomorphic quantum well heterostructures

The well‐width dependence of intersubband transition energies in InGaAs/AlAs pseudomorphic quantum well structures has been studied, and the shortest intersubband wavelength reported to date, 1.798 μm, has been observed for 6 monolayer wells. Both transverse electric and transverse magnetic optical polarizations are absorbed, with an energy splitting of 67 meV between them.

Strain effects in the intersubband transitions of narrow InGaAs quantum wells

Internal uniaxial stress effects on the degenerate P‐like C2 subband Bloch states of Si‐doped (001) InGaAs single quantum wells (SQWs) have been studied using polarization‐resolved infrared spectroscopy. It is found that a tetragonal strain perturbation of the crystal potential produces a splitting between the TM and TE active intersubband transitions. The magnitude of the linear strain intersubband deformation potential of InGaAs quantum wells is 3 eV.

Normal incidence intersubband transitions in Si-doped InGaAs multiple quantum wells

Angle‐ and polarization‐resolved infrared techniques have been used to study the polarization selection rules of intersubband transitions in Si‐doped InGaAs multiple quantum wells (MQWs). Intersubband transitions are found to be active for light, polarized both parallel and perpendicular to the MQW plane, and to show a strain dependent splitting between the corresponding transition energies. Previously reported intersubband data measured in the Brewster angle configuration for the same lattice‐matched and strained Si‐doped InGaAs MQWs were also reproduced.

Absorption spectroscopy on room temperature excitonic transitions in strained layer InGaAs/InGaAlAs multiquantum‐well structures

The physical properties (transition energy, oscillator strength, linewidth, binding energy, and reduced effective mass) of room temperature excitons in compressively strained InGaAs/InGaAlAs multiquantum‐well (MQW) structures as a function of the well width have been investigated for the first time by both absorption measurements and photomodulated transmittance measurements. Photomodulated transmittance spectroscopy has been successfully applied to clearly reveal critical transition points. Measured transition energies are in good agreement with a model which includes the heavy hole and light hole splitting due to the strain. For well widths of 2.5–7.5 nm, oscillator strengths are smaller for the strained layer MQWs than for the lattice‐matched MQWs by 35%–45%. This is due to the larger exciton radius for the strained MQWs resulting from smaller in‐plane reduced effective masses (0.031–0.038m0), which are 65% of those of the lattice‐matched MQWs.

Reply to ‘‘Comment on: ‘Multiband coupling effects on electron quantum well intersubband transitions’ ’’ [J. Appl. Phys. 80, 600 (1996)]

It is shown that the 14 band k⋅p analysis of TE (x,y)‐polarized quantum well intersubband transitions can be categorized as (i) second order (bulk limit), and (ii) first order (quantum limit) perturbation depending on the structures. In the quantum limit, TE‐active intersubband transition prevails. This explains the recent reports of normal incident quantum well photodetectors made of InGaAs/GaAs, InGaAs/AlGaAs, and GaAs/AlGaAs.It is shown that the 14 band k⋅p analysis of TE (x,y)‐polarized quantum well intersubband transitions can be categorized as (i) second order (bulk limit), and (ii) first order (quantum limit) perturbation depending on the structures. In the quantum limit, TE‐active intersubband transition prevails. This explains the recent reports of normal incident quantum well photodetectors made of InGaAs/GaAs, InGaAs/AlGaAs, and GaAs/AlGaAs.

Intrasubband plasmons in delta‐doped InGaAs single quantum wells

Polarization‐resolved infrared techniques have been applied to study the optical properties of the quasi‐two‐dimensional electron gas in doped InGaAs quantum wells and to show that inter‐ and intrasubband processes can be distinguished by their polarization sensitivity. Distinct excitations of inter‐ and intrasubband transitions at the Γ(q=k=0) point in delta‐doped narrow InGaAs/AlAs single quantum wells were resolved through the use of quantum well structures designed to increase their energy difference and thus diminish the coupling between these two processes. Longitudinal qz intrasubband plasmons were observed at 1550 cm−1 and were excited by transverse‐magnetic (TM) polarized light; the intersubband transitions occurred at around 4000 cm−1 and were both transverse‐electric (TE) and TM polarization active.

Defect activated infrared multiphonon excitation in iron-doped semi-insulating indium phosphide

Multiphonon excitation induced by long‐range order crystal‐field and short‐range order Jahn–Teller distortion effects is observed in Fe‐doped semi‐insulating InP in the spectral range from 400 to 1100 cm−1 for infrared light propagating in a slab waveguide geometry. Transmission measurement data are analyzed in terms of phonon energies at critical points in the Brillouin zone. The phonon energies obtained are in excellent agreement with recently reported second order Raman scattering spectra and two‐phonon absorption measurements of crystalline InP. The energy differences between the nearly degenerate two phonon transverse optical+longitudinal optical transitions at the Γ, X, and L points are also resolved and shown to be 10 cm−1. No localized mode or vibronic level absorption is observed, consistent with the relatively low concentration of Fe impurities in the samples.

Spatial confinement effects on type II quantum well intersubband transitions

A study is made of the polarization dependence of intersubband transitions in n+ InP/InAlAs type II quantum wells (QWs), and it is shown that the type II nature of the valence bands and heavy electron band in these QWs is reflected in the spectra. Specifically it is found that the lack of spatial confinement to the QW in the Γ15v valence bands and higher conduction band in InP/InAlAs quantum wells (i) eliminates the coupling between Γc1 conduction subbands and heavy holes and electrons, and (ii) diminishes the normal‐incidence intersubband activity in type II QWs, in accordance with the predictions of a recently published 14‐band k⋅p analysis of quantum well subband levels.