Scientists / Open questions

Herbert Kroemer

Semiconductor physics; heterostructure devices

2000 Nobel Prize in Physics

44 questions

Unresolved center-loading morphology and multi-valley barrier-escape questions in heavily n-doped GaSb–AlSb quantum-well infrared photodetector structures
Quantitative determination of lateral Al segregation and the origin of the polarization redshift in GaSb/AlSb serpentine superlattices
Origin of submicroscopic faceting in MBE growth on GaAs(211)B and the mechanism of the anomalous photoluminescence intensity enhancement in lattice-matched (211) GaAs/(Al,Ga)As superlattices
Controlled phase separation in epitaxial (Ge2)x(GaAs)1-x films: designed quasi-periodic Ge/GaAs stripe architectures and composition-dependent film structure
Microscopic origin of the thermally activated, width-dependent residual resistance in superconductor-coupled InAs quantum-well weak-link arrays
Interface-bonding effects in InAs-AlSb quantum wells: quantitative band-structure description, mechanisms of the photoluminescence energy shift and linewidth, and controlled growth of AlAs-like interfaces
Fluctuation-induced dc resistance of ballistic semiconductor-coupled superconducting weak links: interrupted Andreev-reflection statistics and the width-proportional activation energy
Compensation, defect control, and stability of metastable single-phase $(\mathrm{Ge}_{2})_{x}(\mathrm{GaAs})_{1-x}$ zincblende alloys
Carrier distribution and band lineup at the MBE-grown GaAs/Si(211) heterojunction: validating the quasi-two-dimensional-electron-gas interpretation of the anomalous Hall sheet charge
Screened Peierls instability in a nearly-free-electron quasi-one-dimensional metal: nonperturbative equilibrium, wave-vector selection, and finite-temperature theory
Device-quality GaAs/(Al,Ga)As on (211)-oriented Si with thin superlattice buffer layers: intrinsic FET performance at reduced background doping, optimum buffer thickness, and unresolved material and device characterization (dislocation density, minority-carrier lifetime, lasers, solar cells)
Self-consistent model of the two-subband magnetocapacitance of gated InAs/AlSb quantum wells and the origin of the anomalous shifts of capacitance minima to lower magnetic field
Quantitative low-temperature mobility limits of undoped two-dimensional hole gases in (In)GaSb/AlSb quantum wells: separating native-defect, interface-roughness, and remote-charge scattering, and the headroom from defect reduction
Making capacitance-voltage profiling a reliable method for conduction-band-offset extraction in polar III-nitride heterostructures: sub-nanometer interface location and unexplained reconstruction discrepancies
Open issues in the quantitative quasiparticle-dynamics theory of the anomalous ac Josephson effect in ballistic superconducting weak links
Verifying the antimony-added InAlGaAs flat-valence-band prediction for low-voltage p-type AlAsSb distributed Bragg reflectors, and demonstrating InAlGaAs/AlAsSb mirrors in electrically-pumped 1.55 um VCSELs
Validated composition dependence of the band-gap and band-edge energies of lattice-matched GaInAsSb/GaSb and GaInAsSb/InAs alloys: short-range-order, clustering, and temperature effects
Direct experimental verification of the arsenic-on-aluminum-site antisite donor model at AlAs-like bottom interfaces of AlSb/InAs/AlSb quantum wells, and quantitative attribution of the associated mobility degradation
General reconstruction of the true carrier profile from the Debye-averaged apparent profile in C-V profiling of semiconductors
Unquantified polarization and doping-gradient corrections in capacitance-voltage profiling of heterojunction band offsets
Microscopic origin of residual dissipation in Nb-contacted InAs quantum-well weak-link arrays
Microscopic quantitative origin of the above-gap conductance dip and zero-bias Andreev peak in Nb-contacted InAs-AlSb quantum wells
Unresolved deep levels in Te-doped AlSb and the Al-rich composition dependence of the Te deep donor in AlxGa1−xSb
Direct experimental band alignment and interface charge of nonpolar m-plane (10-1̄0) and semipolar (20-2̄1) GaN/AlGaN heterojunctions

Back to open problems

Unresolved center-loading morphology and multi-valley barrier-escape questions in heavily n-doped GaSb–AlSb quantum-well infrared photodetector structures

Quantitative determination of lateral Al segregation and the origin of the polarization redshift in GaSb/AlSb serpentine superlattices

Origin of submicroscopic faceting in MBE growth on GaAs(211)B and the mechanism of the anomalous photoluminescence intensity enhancement in lattice-matched (211) GaAs/(Al,Ga)As superlattices

Controlled phase separation in epitaxial (Ge2)x(GaAs)1-x films: designed quasi-periodic Ge/GaAs stripe architectures and composition-dependent film structure

Microscopic origin of the thermally activated, width-dependent residual resistance in superconductor-coupled InAs quantum-well weak-link arrays

Interface-bonding effects in InAs-AlSb quantum wells: quantitative band-structure description, mechanisms of the photoluminescence energy shift and linewidth, and controlled growth of AlAs-like interfaces

Fluctuation-induced dc resistance of ballistic semiconductor-coupled superconducting weak links: interrupted Andreev-reflection statistics and the width-proportional activation energy

Compensation, defect control, and stability of metastable single-phase (Ge2)x(GaAs)1−x(\mathrm{Ge}_{2})_{x}(\mathrm{GaAs})_{1-x}(Ge2​)x​(GaAs)1−x​ zincblende alloys

Carrier distribution and band lineup at the MBE-grown GaAs/Si(211) heterojunction: validating the quasi-two-dimensional-electron-gas interpretation of the anomalous Hall sheet charge

Screened Peierls instability in a nearly-free-electron quasi-one-dimensional metal: nonperturbative equilibrium, wave-vector selection, and finite-temperature theory

Device-quality GaAs/(Al,Ga)As on (211)-oriented Si with thin superlattice buffer layers: intrinsic FET performance at reduced background doping, optimum buffer thickness, and unresolved material and device characterization (dislocation density, minority-carrier lifetime, lasers, solar cells)

Self-consistent model of the two-subband magnetocapacitance of gated InAs/AlSb quantum wells and the origin of the anomalous shifts of capacitance minima to lower magnetic field

Quantitative low-temperature mobility limits of undoped two-dimensional hole gases in (In)GaSb/AlSb quantum wells: separating native-defect, interface-roughness, and remote-charge scattering, and the headroom from defect reduction

Making capacitance-voltage profiling a reliable method for conduction-band-offset extraction in polar III-nitride heterostructures: sub-nanometer interface location and unexplained reconstruction discrepancies

Open issues in the quantitative quasiparticle-dynamics theory of the anomalous ac Josephson effect in ballistic superconducting weak links

Verifying the antimony-added InAlGaAs flat-valence-band prediction for low-voltage p-type AlAsSb distributed Bragg reflectors, and demonstrating InAlGaAs/AlAsSb mirrors in electrically-pumped 1.55 um VCSELs

Validated composition dependence of the band-gap and band-edge energies of lattice-matched GaInAsSb/GaSb and GaInAsSb/InAs alloys: short-range-order, clustering, and temperature effects

Direct experimental verification of the arsenic-on-aluminum-site antisite donor model at AlAs-like bottom interfaces of AlSb/InAs/AlSb quantum wells, and quantitative attribution of the associated mobility degradation

General reconstruction of the true carrier profile from the Debye-averaged apparent profile in C-V profiling of semiconductors

Unquantified polarization and doping-gradient corrections in capacitance-voltage profiling of heterojunction band offsets

Microscopic origin of residual dissipation in Nb-contacted InAs quantum-well weak-link arrays

Microscopic quantitative origin of the above-gap conductance dip and zero-bias Andreev peak in Nb-contacted InAs-AlSb quantum wells

Unresolved deep levels in Te-doped AlSb and the Al-rich composition dependence of the Te deep donor in AlxGa1−xSb

Direct experimental band alignment and interface charge of nonpolar m-plane (10-1̄0) and semipolar (20-2̄1) GaN/AlGaN heterojunctions

Compensation, defect control, and stability of metastable single-phase $(\mathrm{Ge}_{2})_{x}(\mathrm{GaAs})_{1-x}$ zincblende alloys