Δ-doped GaAs Layers Research Articles

Metastability and Electronic Structure of Periodically n-Type and p-Type δ-Doped Layer in GaAs

Metastability and Electronic Structure of Periodically n-Type and p-Type δ-Doped Layer in GaAs

Nonlinear electron transport in Si δ-doped GaAs

In this paper we report abnormal non-ohmic behaviour observed in Si δ-doped GaAs. We have performed measurements in Hall bar and Van der Pauw geometries in which electron transport phenomena can be studiekd by looking into the dependence of the device resistance Rxx on the applied current I or input power per electron, P. Transport of electrons in single Si δ-doped layers in GaAs, grown by MOCVD, in the linear and non-linear response regimes was studied. Our experimental results show that: i) Rxx dramatically decreases with increasingI (P) when sample current (input power) is larger than a critical value Ic (Pc); ii) Ic increases with electron density (Si δ-doping concentration); and iii) the decrease in Rxx with increasing I in the non-linear response regime can be observed both at zero and high magnetic fields over a wide temperature range. When Rxx is plotted as a function of the power loss rate per electron (P) the values of the critical power (Pc) for different samples are roughly the same. We suggest that redistribution of the ionised donors in the sample occurring when I >Ic takes the major responsibility for the observed abnormal phenomena.

Quasi-two-dimensional plasmons of a single delta -doped layer in GaAs studied by high-resolution electron-energy-loss spectroscopy.

High-resolution electron-energy-loss spectroscopy (HREELS) is used to study δ-doped GaAs samples with varying silicon dopant concentration. The δ-doped layers were grown by molecular-beam epitaxy at a substrate temperature of 600 o C and the silicon atoms were incorporated 20 nm underneath the surface. Characteristic loss structures are observed in the HREEL spectra and are attributed to the excitation of quasi-two-dimensional (2D) plasmon modes confined to the 6-doped region. A three-layer model of a confined free-electron gas is presented to understand the nature of the quasi-2D plasmon loss features

Electronic properties of multiple Si δ-doped GaAs layers grown by molecular beam epitaxy and migration-enhanced epitaxy

We report on comparative measurements of the electronic properties of multiple Si δ-doped GaAs structures grown by conventional molecular beam epitaxy (MBE) and by migration-enhanced epitaxy (MEE) at a substrate temperature of 540°C. Samples were studied by Shubnikov-De Haas and Hall measurements. Results suggest that for multiple δ-doped samples grown at high substrate temperatures, MBE is a more effective growth technique.

Fermi edge singularity and screening effects in the luminescence spectra of Si or Be δ-doped GaAs

Single Si or Be δ-doped layers in GaAs have been investigated by photoluminescence (PL) and photoluminescence excitation spectroscopy (PLE). Strong radiative recombination is observed from the two-dimensional electron or hole gas when the photocreated minority carriers are confined by GaAs/Al x Ga 1 − x As heterointerfaces placed at both sides of the doping spike. In n-type δ-doped structures the low-temperature PLE spectrum shows a well resolved Fermi edge enhancement with the energy position of the absorption edge independent of the excitation intensity. The spatially indirect band-to-band recombination, in contrast, is found to shift to higher energies with increasing excitation intensities due to screening of the space charge induced potential by photogenerated carriers. In the p-type δ-doped structure the low-temperature emission from the two-dimensional hole gas shows a pronounced enhancement in intensity at the Fermi edge.

The Confining Potential for Carriers in Planar Doped GaAs and the Effect of Photoexcitation

ABSTRACTSingle Be and Si δ-doped layers in GaAs have been investigated by Raman spectroscopy. GaAs/AlxGa1-xAs heterointerfaces, placed 30nm from the dopant spike on either side, facilitate optical measurements by the confinement of photogenerated minority carriers. Self-consistent subband calculations have been performed to compute the subband structure of the two-dimensional electron or hole gas which is confined by the space-charge induced potential well at the δ-doping layer. Upon increasing photoexcitation, the increase in density of photocreated electrons in the Be structure is clearly seen in the polarised Raman scattering spectrum by the appearance, and subsequent increase in frequency, of the electron plasmon modes. The electric field at the top GaAs/AlxGa1-xAs interface is monitored by measuring the strength of electric field induced LO phonon scattering.

Electronic properties of multiple Si δ doping in GaAs

The subband structure of multiple Si δ-doped layers in GaAs is calculated within the local-density-functional approximation for several doping periods. The diffusion effect of donors impurities are investigated. The physical properties of the present multiple δ doping depend strongly on the period length, reflecting a transition from quantum well to superlattice.

Variation of the mobility and the two-dimensional electron gas concentration with indium composition in δ-doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures

The electron mobility and the two-dimensional electron gas (2DEG) concentration in different indium compositions (0.1<x<0.6) δ-doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures grown by low-pressure metalorganic chemical vapor deposition are studied. The electron mobilities of a δ-doped GaAs layer are comparable to those of previous reports. Furthermore, the maximum mobility (5500 and 33 000 cm2/V s at 300 and 77 K, respectively) of the proposed pseudomorphic structure appears at x=0.37. Taking into account of strain and quantum effects, the variation trends of calculated 2DEG concentrations are in good agreement with the experimental results.

Electron energy levels in a delta -doped layer in GaAs.

Calculated results for energy levels of electrons in a Si \ensuremath{\delta}-doped layer in GaAs are presented at T=0 K and ambient temperature. Their sensitivity to the donor distribution is examined. The many-body exchange-correlation effects are taken into account in the local-density-functional approximation.

Fermi edge singularity and screening effects in the absorption and luminescence spectrum of Si δ-doped GaAs

We have investigated single Si δ-doped layers in GaAs by photoluminescence and photoluminescence excitation spectroscopy (PLE). When the photogenerated holes are confined by GaAs/AlxGa1−xAs heterointerfaces placed at either side of the doped layer strong radiative recombination is observed from the quasi-two-dimensional electron gas associated with the δ-doping spike. The low-temperature absorption spectrum involving spatially direct transitions, which was measured by PLE, shows a well resolved enhancement at the Fermi edge. The energy position of the absorption edge is found to be independent of the excitation intensity. The peak energy of the band-to-band emission spectrum, in contrast, which involves spatially indirect transitions, shows a shift to higher energies with increasing excitation intensity due to the screening of the space-charge-induced potential by photogenerated carriers.

A quantum well δ-doped GaAs FET fabricated by low-pressure metal organic chemical vapor deposition

A quantum well δ-doped n-type GaAs layer with Ga source open has been grown successfully by the low-pressure metal organic chemical vapor deposition (LP-MOCVD). The measured capacitance-voltage profile shows that a sheet-doping concentration up to 5 × 10 12 cm −2 for the δ-doped GaAs layer can be easily achieved. The full-width at half-maximum (FWHM) is quite narrow. From the Hall measurement, the electron mobility increases inversely proportional to the δ-doping concentration. An enhanced mobiity can be obtained more than 2300 and 4300 cm 2/Vs with doping concentration of 5.0 × 10 18 cm −3 at 300 and 77 K, respectively. Based on this technique, a quantum well δ-doped GaAs FET has been fabricated and demonstrated. With a gate geometry of 5 × 250 μm 2 and doping concentration of 5.9 × 10 18 cm −3, the estimated transconductance of the δ-doped FET is 64 mS/mm. Since there is an undoped GaAs layer grown on the top of the δ-doped sheet, the breakdown voltage can be increased significantly (> 17 V). Furthermore, the saturation current density can be obtained higher than 110 mA/mm.

Photoluminescence from the quasi-two-dimensional electron gas at a single silicon delta -doped layer in GaAs.

Radiative recombination of quasi-two-dimensional electrons with photocreated holes is reported in single silicon \ensuremath{\delta}-doped layers in GaAs. These holes are confined within the GaAs surface and the potential induced by the doping spike, which is repulsive for holes. Replacing the GaAs surface by an ${\mathrm{Al}}_{0.33}$${\mathrm{Ga}}_{0.67}$As/GaAs heterointerface the photoluminescence from the \ensuremath{\delta}-doping spike is drastically enhanced. It is shown by photoluminescence and Raman spectroscopy that the density of carriers created by cw photoexcitation can be made sufficiently high in the heterostructure to modify the actual shape of the doping-induced potential well.

Interband transitions of Si ?-doped layers in p-Type GaAs

The two-dimensional (2D) electron gas present in Si δ-doped layers in p-type GaAs is investigated through photoreflectance (PR) measurements performed at 300 and 77 K. The obtained spectra show oscillatory structures above the GaAs band gap which are ascribed to Franz–Keldysh oscillations. The decrease in the energy differences of the oscillations extrema with temperature indicates a reduction of the built-in electric field in the δ-doped region. The values of the electric field extracted from the experimental data are compared with those obtained from theoretical calculations based on a simultaneous self-consistent solution of the Schrodinger and Poisson equations. The agreement between theory and experiment strongly indicate that the observed oscillatory structures in the PR spectra are due to transitions to electron states of the 2D electron gas.

Direct imaging of δ-doped layers in GaAs

We report the direct imaging of Be δ-doped layers in GaAs, in the concentration range (0.5–2)×1014/cm2, comparing samples grown by gas source molecular beam epitaxy (MBE) and conventional MBE. The gas source MBE δ layers are ∼15 Å wide, and at least at high concentrations, consist of clusters ∼12 Å in diameter. At 2×1014 Be atoms/cm2, the MBE δ layer is an order of magnitude wider than that grown at the same temperature by gas source MBE. Our results imply that layers with Be concentrations in excess of 1021/cm3 can be fabricated by gas source MBE.

Continuous to bound interband transitions in δ-doped GaAs layers

We have studied the interband transitions of several silicon δ-doped GaAs samples using the technique of photoreflectance spectroscopy. The features observed in the optical spectra above the GaAs fundamental energy gap are tentatively attributed to transitions involving continuous valence band states and quantum-confined states at the conduction-band. The observed interband transition energies are in qualitative agreement with the self-consistently calculated ones taking into account the spreading of dopants.

Incorporation of Si in δ-doped GaAs studied by local vibrational mode spectroscopy

Raman scattering by local vibrational modes has been used to study the incorporation of Si in single δ-doped GaAs layers. Placing the doping spike at different depths underneath the surface, a depth profile of the dopant concentration incorporated on lattice sites has been obtained. For samples grown by molecular beam epitaxy under conditions which are known to lead to a significant broadening of the doping spike, the applied Raman technique reveals the incorporation of Si on Ga sites with a broadening of the Si distribution in excess of 20 nm.