Layered Semiconductor Structures Research Articles

Strain in layered zinc blende and wurtzite semiconductor structures grown along arbitrary crystallographic directions

We present a simple approach to the evaluation of strain in zinc blende and in wurtzite layered semiconductor structures. These crystallographic structures are of particular interest because of their importance in optoelectronic device applications. The composite layered materials are currently grown pseudomorphically on substrates, which dictate the strain in the layers. Components of the strain are derived for arbitrary crystallographic growth directions. The strain in the layer determines the piezoelectric field in each layer in the structure. The strain and the strain-induced electric field are important in designing layered heterostructures with specific electronic energy levels for device applications. The methods presented are more generally applicable to other crystallographic structures and composite pseudomorphically grown materials. Illustrative problems and solutions are included.

A study on the thermomechanical behavior of semiconductor chips on thin silicon substrate

This study is concerned with the deformation or warping behavior of thin layered semiconductor structure comprising a silicon substrate, a pattern layer and a polyimide coating layer with its thickness varying from 100um to 50 um. In contrast with the conventional thick semiconductor structure, today’s semiconductor structure is increasingly thin and therefore the warping is extremely conspicuous, being among the major concerns in the structural design of a chip. In the view of thermomechanical analysis of an extremely thin layer structure considered in the present paper, a few parameters on the deformation should be taken into consideration such as the pattern layer and intrinsic stress. To account for the effect of the pattern layer, we make a well educated guess for the mechanical properties, employing the test results and the CBA (Composite Beam Analysis) theory. In addition, we take into consideration the effect of the intrinsic stress due to moisture absorption on deformation. We show that the chip warpage is accurately predicted when all these are properly considered. Furthermore, we have found that the local instability or wrinkling, associated with the nonuniformity or the inhomogeneity in material properties and bonding quality between any two neighboring layers, appears as one important mode of energy relaxation in addition to the overall warpage when the chip thickness becomes very small.

The optical Hall effect

AbstractClassic electrical Hall effect measurements are standard for electrical characterization of free charge carriers in semiconductor layer structures. We demonstrate that magnetooptic generalized ellipsometry at long wavelengths when applied to conducting or semiconducting multilayer or nanoscopically in‐homogeneous structures can yield equivalent and even much increased information. We term this new method optical Hall effect, because it finds simple explanation within the model described by E. H. Hall for the occurrence of the transverse and longitudinal voltages augmented by non‐locality of the charge response in time. Transverse and longitudinal birefringence cause magnificent anisotropic polarization responses unraveling rich information on free charge properties of complex‐structured samples due to external magnetic fields and collective movement of bound and unbound charge carriers. We demonstrate that with our technique density, type, mobility, effective mass including anisotropy can be measured without any electrical contact in buried structures, and which may have been inaccessible to any true electrical evaluation thus far. We predict a realm of applications for the optical Hall effect in future materials research and engineering. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of amplitude characteristics of quantum photodetectors with a large photosensitive area

Pulse amplitude distributions of avalanche photodetectors with a metal-resistive layer-semiconductor structure and a 7-mm2 photosensitive area are investigated in the photon-counting mode. It is shown that p-n junction heterogeneities in a space charge region affect the shape of amplitude distributions of photocurrent pulses, as the overvoltage increases and light spot changes its position on the photosensitive area. The comparative analysis of the amplitude characteristics of the above avalanche photodetectors and commercial ΦД-115д avalanche photodiodes is conducted.

Determination of ‘bisotropic’ stresses in layered semiconductor structures from Raman lightscattering data

Explicit expressions are derived for phonon frequency shifts observed in Ramanexperiments under conditions of isotropic biaxial (‘bisotropic’) stress in the planeof a (111)-oriented cubic crystal. Like in the well-studied case of (001)-orientedcrystal, a phonon doublet and a phonon singlet are formed. But as distinct fromthe (001) crystal orientation case, where the singlet outstrips the doublet withincrease in stress, in the case of (111) orientation, in contrast, the doublet outstripsthe singlet. In the latter case the effect as a whole is quantitatively smaller. Inaddition, in both cases, exclusively simple formulae are obtained which allow theexpression of Raman shifts under bisotropic stress in terms of shifts under uniaxialdeformations of the same material. In this approach one does not need to know inadvance both phonon deformation potentials and elastic constants of the material.

Laudatio for Klaus H. Ploog

Laudatio for Klaus H. Ploog

Monolithically integrated near-infrared and mid-infrared detector array for spectral imaging

A multi-band focal plane array sensitive in near-infrared (near-IR) and mid-wavelength infrared (MWIR) is been developed by monolithically integrating a near-infrared (1–1.5μm) p–i–n photodiode with a mid-infrared (3–5μm) QWIP. This multiband detector involves both intersubband and interband transitions in III–V semiconductor layer structures. Each detector stack absorbs photons within the specified wavelength band, while allowing the transmission of photons in other spectral bands, thus efficiently permitting multiband detection. Monolithically grown material characterization data and individual detector test results ensure the high quality of material suitable for near-infrared/QWIP dual-band focal plane array.

Numerical simulation of time resolved charge transport in semiconductor structures for electronic devices

Excess charge carrier transport and relaxation in semiconductor layered structures have been numerically simulated by a finite-difference method.

Wavefunction engineering of layered wurtzite semiconductors grown along arbitrary crystallographic directions

The electronic band structure of wurtzite semiconductor heterostructures is investigated theoretically using the envelope function k ⋅ P formalism. We use a Lagrangian formulation for the valence bands so that the order of the derivatives appearing in the multiband description is explicitly specified when Schrödinger’s equations for the envelope functions are generated through the application of the principle of least action. The issues of derivative operator ordering and boundary conditions at material interfaces are examined in detail. The theoretical results are presented for arbitrary growth directions and the spin–orbit interaction is taken into account. This is of interest, for example, in treating A -plane wurtzite heterostructures such as GaN/AlGaN quantum wells grown on R -plane sapphire. Strain effects are included using a general rotation method that diagonalizes strain and is appropriate for pseudomorphic wurtzite structures in any allowed orientation. It is shown that inversion asymmetry in the valence band leads to shifts in the band-edge energies in the [ 11 2 ¯ 0 ]-grown quantum wells. The finite element method is used with the Lagrangian for the composite layered semiconductor structure in order to obtain the energy eigenvalues for multi-quantum well systems. Calculations for quantum wells and superlattices are presented.

Long-wavelength interface modes in semiconductor layer structures

We address and explain the occurrence of bulk and interface modes in zinc-blende group-III--group-V semiconductor layer structures observed by spectroscopic ellipsometry at infrared wavelengths. Fano- and Brewster-type transverse-magnetic ($p$-polarized) interface modes as well as transverse-electric ($s$-polarized) surface-guided interface modes are assigned by solutions of the surface polariton dispersion relations for polar semiconductor layer structures. We show that the Berreman-effect [D. W. Berreman, Phys. Rev. 130, 2193 (1963)] is associated with the occurrence of a Fano-interface polariton. Experimental verification is demonstrated for a GaAs homostructure, which consists of differently Te-doped $n$-type substrates covered by undoped epilayers.

Optical vidicon based on a layered semiconductor structure: Image reading and storage

A simple device for image scanning and storage based on a semiconductor structure is proposed. The scanning and storage involve laser-beam reading. A video signal is represented by the photoelectromotive force generated by the structure. Simple experiments demonstrating that the structure proposed works as a vidicon and a storage device capable of the data storage for at least two hours are presented. A physical interpretation of the effects observed is proposed.

On possible spin injection at non-ideal Schottky contacts

The role of the tunneling mechanisms in metal-disordered layer-semiconductor structure under spin injection at the interface is investigated. The non-ideal metal-semiconductor structure as prepared by ionized cluster beam deposition is considered, and it is shown that the depletion region of the semiconductor can be tailored to include a suitably heavily doped region near the interface. The tunneling is described within a simplified model in which the expression for the interface resistance of the metal-disordered layer-semiconductor structure is obtained. It is argued that in the case of ionized cluster beam deposited non-ideal Schottky structure a significant spin injection is achieved.

Waveguide design for mid- and far-infrared p-Si/SiGe quantum cascade lasers

Design considerations are presented for waveguides to be used in p-Si/SiGe based quantum cascade lasers operating in the mid- and far-infrared wavelength ranges. Modal losses and confinement factors are calculated for both TM and TE modes in conventional double metal clad structures, metal–highly doped semiconductor layer structures and also in novel metal–metal silicide structures. Guidelines for choosing the confinement and contact layer parameters are given.

Dispersion and instability of electromagnetic waves in layered periodic semiconductor structures

The effect of carrier drift on the dispersive properties and instability of electromagnetic waves and plasma polaritons in infinite layered periodic semiconductors are considered. It is assumed that in similar semiconductor layers, carriers drift parallel to the interfaces. Drift waves are shown to have a specific band structure of the spectrum. The dispersive properties of collective plasma polaritons under drift are considered, the instability of the polaritons and drift waves is studied, and the instability increments are determined.

Generalized far-infrared magneto-optic ellipsometry for semiconductor layer structures: determination of free-carrier effective-mass, mobility, and concentration parameters in n-type GaAs.

We report for the first time on the application of generalized ellipsometry at far-infrared wavelengths (wave numbers from 150 cm(-1) to 600 cm(-1)) for measurement of the anisotropic dielectric response of doped polar semiconductors in layered structures within an external magnetic field. Upon determination of normalized Mueller matrix elements and subsequent derivation of the normalized complex Jones reflection matrix r of an n-type doped GaAs substrate covered by a highly resistive GaAs layer, the spectral dependence of the room-temperature magneto-optic dielectric function tensor of n-type GaAs with free-electron concentration of 1.6 x 10(18) cm(-3) at the magnetic field strength of 2.3 T is obtained on a wavelength-by-wavelength basis. These data are in excellent agreement with values predicted by the Drude model. From the magneto-optic generalized ellipsometry measurements of the layered structure, the free-carrier concentration, their optical mobility, the effective-mass parameters, and the sign of the charge carriers can be determined independently, which will be demonstrated. We propose magneto-optic generalized ellipsometry as a novel approach for exploration of free-carrier parameters in complex organic or inorganic semiconducting material heterostructures, regardless of the anisotropic properties of the individual constituents.

Superfast fronts of impact ionization in initially unbiased layered semiconductor structures

A mode of impact ionization breakdown of a p–n junction is suggested: We demonstrate that when a sufficiently sharp voltage ramp is applied in reverse direction to an initially unbiased equilibrium p+–n–n+ structure, after some delay the system will reach a high conductivity state via the propagation of a superfast impact ionization front. The front travels towards the anode with a velocity vf several times larger than the saturated drift velocity of electrons vs leaving a dense electron–hole plasma behind. The excitation of the superfast front corresponds to the transition from the common avalanche breakdown of a semiconductor structure to a collective mode of streamer-like breakdown. We propose that similar fronts can be excited not in layered structures but in plain bulk samples without p–n junctions. Our numerical simulations apply to a Si structure with typical thickness of W∼100 μm switched in series with a load R∼100 Ω, with a voltage ramp of A>1012 V/s applied to the whole system. Our simulations show that first there is a delay of about 1 ns during which the voltage reaches a value of several kilovolts. Then, as the front is triggered, the voltage abruptly breaks down to several hundreds of volts within ∼100 ps. This provides a voltage ramp of up to ∼2×1013 V/s hence up to 10 times sharper than the externally applied ramp. We unravel the source of initial carriers which trigger the front, explain the origin of the time delay in triggering the front, and we identify the mechanism of front propagation.

Tunneling-assisted impact ionization fronts in semiconductors

We discuss a type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp (∼10 kV/ns) is applied in reverse direction to a Si p+–n–n+ structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns. The maximal electrical field at the front edge exceeds 106 V/cm. The front velocity vf is 40 times faster than the saturated drift velocity vs. The front passes through the n-base with a thickness of 100 μm within approximately 30 ps, filling it with dense electron–hole plasma. This passage is accompanied by a voltage drop from 8 kV to a voltage in the order of 10 V. In this way a voltage pulse with a ramp up to 500 kV/ns can be applied to the load. The possibility to create a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.

Far-infrared magnetooptical generalized ellipsometry determination of free-carrier parameters in semiconductor thin film structures

ABSTRACTIn accord with the Drude model, the free-carrier contribution to the dielectric function at infrared wavelengths is proportional to the ratio of the free-carrier concentration N and the effective mass m*, and the product of the optical mobility μ and m*. Typical infrared optical experiments are therefore sensitive to the free-carrier mass, but determination of m* from the measured dielectric function requires an independent experiment, such as an electrical Hall-effect measurement, which provides either N or μ. Highly-doped zincblende III-V-semiconductors exposed to a strong external magnetic field exhibit non-symmetric magnetooptical birefringence, which is inversely proportional to m*. If the spectral dependence of the magnetooptical dielectric function tensor is known, the parameters N, m* and μ can be determined independently from optical measurements alone. Generalized ellipsometry measures three complex-valued ratios of normalized Jones matrix elements, from which the individual tensor elements of the dielectric function of arbitrarily anisotropic materials in layered samples can be reconstructed. We present the application of generalized ellipsometry to semiconductor layer structures at far-infrared wavelengths, and determine the magnetooptical dielectric function for n-GaAs and n-AlGaInP for wavelengths from 100 μm to 15 μm. We obtain the effective electron mass and mobility results of GaAs in excellent agreement with results obtained from Hall-effect and Shubnikov-de-Haas experiments. The effective electron mass in disordered n-AlGaInP obtained here is in very good agreement with previous k·p calculations. (Far)-infrared magnetooptic generalized ellipsometry may open up new avenues for non-destructive characterization of free-carrier properties in complex semiconductor heterostructures.

Quasi-Electric Fields and Band Offsets: Teaching Electrons New Tricks (Nobel Lecture)

The invention and development of fast opto- and microelectronic components based on layered semiconductor structures, termed semiconductor heterostructures, is described herein. Such fast transistors are used in radio link satellites and the base stations of mobile telephones, for examples. Laser diodes built with the same technology drive the flow of information along fiber-optic cables, and may be found also in CD players, bar-code readers, and laser pointers. The double-heterostructure principle is also increasingly used in incoherent light-emitting diodes, for example in traffic lights and other light sources requiring colored visible light.

Makyoh topography for the morphological study of compound semiconductor wafers and structures

The application of Makyoh topography in the assessment of flatness and overall curvature of semiconductor wafers and layer structures is reviewed, with special emphasis on compound semiconductors. Application examples are shown as well.