Total Trap Concentration Research Articles

Characterization of high-purity Si-doped molecular beam epitaxial GaAs

High-purity, lightly Si-doped (μ77∼70 000–126 000 cm2/V s and n77∼2–8×1014 cm−3) molecular beam epitaxy (MBE) GaAs layers have been characterized using variable-temperature Hall effect and C-V measurements, photothermal ionization spectroscopy, low-temperature photoluminescence (PL), and deep level transient spectroscopy (DLTS). The spectroscopic measurements of the residual donors and acceptors indicate that the pronounced increase in carrier concentration which is observed with increasing As flux (for a constant Ga flux) results from incorporation of additional residual S donors from the As source material, and not from reductions in the Si acceptor concentration or residual C acceptor concentration. The increase in carrier concentration with As flux is considerably more pronounced when using an alternative source of As, which introduces both S and 3 additional donor species. The C acceptor concentration increases with As flux using either As source, although the increase is much stronger with the alternative source. The dependence of C concentration on the As source implies that the As source itself contributes at least part of the C background. The Si acceptor concentration is negligible for the range of growth conditions that were used. Close compensation between the residual S donors and C acceptors may account for the high resistivity previously observed in undoped samples grown in this system using the purer As source. The PL data exhibit very weak ‘‘defect’’-related emissions in the 1.504–1.512 and 1.466–1.482 eV ranges; evidence is presented supporting the existence of a correlation between these two sets of peaks, in agreement with the work of Briones and Collins. Temperature and excitation intensity-dependent PL measurements are used to demonstrate conclusively that the peaks in the 1.466–1.482 eV range are donor-to-acceptor and band-to-acceptor in nature, involving normal shallow donors and at least four different acceptor levels whose exact origin is unknown. The ‘‘defect’’ peak intensity is larger in the less pure material which contains more C, implying that the ‘‘defects’’ may be C related. Several electron traps including M1, M3, and M4 are observed in the DLTS spectra, and the C-V measurements give a total trap concentration of ∼3×1013 cm−3.

An electron-trapping defect level associated with the 235K annealing stage in electron-irradiation n-GaAs

The authors report measurements by deep-level transient spectroscopy (DLTS) and immobile-space-charge profiling on lattice-defect production in VPE n-GaAs at 80K by 1.0 MeV electron irradiation, and on the annealing behaviour of the defects at 80-300K. It is shown that the electron traps E1, E2 and E3 are produced by the irradiation, before anneal at 300K, and that an additional electron-trapping defect 'E(0.23)', with an apparent activation energy of 0.23+or-0.02 eV to the conduction band, is created by the irradiation and is removed in the 235K annealing stage found previously by Thommen (1970) in electron-irradiated bulk-grown n-GaAs. The authors suggest that the E(0.23) level arises from a plural-defect structure, and that it anneals by dissociation or internal recombination. The results also indicate the irradiation production of below-mid-gap electron-trapping levels at a concentration much larger than the concentration of electron traps observed, as DLTS levels, in the upper half of the energy gap, and that about 50% annealing of the total net electron trap concentration occurred at 80-300K. Increased at 80-300K in the concentrations of the E1 and E2 defects were also observed in this range of annealing temperature.

GaInP grown by molecular beam epitaxy doped with Be and Sn

Using an ancillary flux of Pb atoms, we have grown Be-doped Ga0.5In0.5P on (001) GaAs substrates by molecular beam epitaxy (MBE) with hole concentrations as low as 1016 cm−3, a region previously inaccessible by conventional MBE growth. Sn-doped layers have also been grown by the same technique with similar concentrations of electrons. Room temperature hole mobilities exceed literature values for VPE layers. Deep level spectra have revealed three electron traps with thermal activation energies of 0.15, 0.34, and ∼0.81 eV. The total electron trap concentration was 5.2×1015 cm−3 in a layer with n = 5×1016 cm−3. The dominant mid-gap trap was also detected in n-type layers grown without the Pb flux. The concentration of Pb incorporated in the layer is about 1.5×1017 cm−3 and is uniformly distributed. This corresponds to about 2×10−4 of the incident Pb flux. The presence of Pb on the surface induces a change from a weak 2×1 RED pattern to a sharp 1×2 pattern and we suppose that this modification of the surface structure reduces the concentration of deleterious defect centers.