Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

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Luminescence properties of defects in GaN

An overview of ohmic contacts on solar cells is presented The fundamentals of metal-semiconductor contacts are reviewed, including the Schottky approach, Fermi level pinning by surface states, and the mechanisms of thermionic emission, thermionic/field emission, and tunneling for current transport The concept of contact resistance is developed and contact resistance data for several different contact materials on both silicon and gallium arsenide over a range of doping densities are summarized Finally, the requirements imposed by solar cells on contact resistance are detailed

Solar cell contact resistance&#8212;A review

Most metal–semiconductor contacts are rectifying. For moderately doped semiconductors, the current transport across such Schottky contacts occurs by thermionic emission over the Schottky barrier. The current–voltage characteristics of real Schottky contacts are described by two fitting parameters that are the effective barrier heights ΦBeff and the ideality factors n. Due to lateral inhomogeneities of the barrier height, both parameters differ from one diode to another. However, their variations are correlated in that ΦBeff becomes smaller with increasing n. Extrapolations of such ΦBeff-versus-n plots to the corresponding image-force-controlled ideality factors nif give the barrier heights of laterally homogeneous contacts. They are then compared with the theoretical predictions for ideal Schottky contacts. Data of Si, GaN, GaAs, and CdTe Schottky contacts reveal that the continuum of metal-induced gap states is the fundamental mechanism that determines the barrier heights. However, there are additional b...

Barrier heights of real Schottky contacts explained by metal-induced gap states and lateral inhomogeneities

GaAs layers grown by molecular beam epitaxy (MBE) at substrate temperatures between 200 and 300 °C were studied using transmission electron microscopy (TEM), x‐ray diffraction, and electron paramagnetic resonance (EPR) techniques. High‐resolution TEM cross‐sectional images showed a high degree of crystalline perfection of these layers. For a layer grown at 200 °C and unannealed, x‐ray diffraction revealed a 0.1% increase in the lattice parameter in comparison with bulk GaAs. For the same layer, EPR detected arsenic antisite defects with a concentration as high as 5×1018 cm−3. This is the first observation of antisite defects in MBE‐grown GaAs. These results are related to off‐stoichiometric, strongly As‐rich growth, possible only at such low temperatures. These findings are of relevance to the specific electrical properties of low‐temperature MBE‐grown GaAs layers.

Structural properties of As‐rich GaAs grown by molecular beam epitaxy at low temperatures

The feasibility of producing erbium‐doped silicon light‐emitting diodes by molecular beam epitaxy is demonstrated. The p‐n junctions are formed by growing an erbium‐doped p‐type epitaxial silicon layer on an n‐type silicon substrate. When the diodes are biased in the forward direction at 77 K they show an intense sharply structured electroluminescence spectrum at 1.54 μm. This luminescence is assigned to the internal 4f–4f transition 4I13/2→4I15/2 of Er3+ (4f11).

1.54‐μm electroluminescence of erbium‐doped silicon grown by molecular beam epitaxy

AsGa antisite defects formed during plastic deformation of GaAs are identified by electron paramagnetic resonance (EPR) measurements. From photo‐EPR results it can be concluded that the two levels of this double donor are located near Ec −0.75 eV and Ev +0.5 eV. These values are coincident with the Fermi level pinning energies at Schottky barriers. The upper level can be related to the ’’main electron trap’’ EL2 in GaAs. Photoluminescence experiments before and after thermal annealing suggest that AsGa defects reduce the near band edge luminescence efficiency. A dislocation climb model is presented which is able to explain AsGa formation during dislocation movement. The production of AsGa antisites during dislocation motion under injection conditions in light emitting devices may thus be connected with degradation of the light output.

Identification of AsGa antisites in plastically deformed GaAs

Rare earth activated luminescence in InP, GaP and GaAs

The annealing behavior of the 08 eV luminescence band in undoped semiinsulating GaAs has been investigated It is found to be fully analogous to that of the AsGa antisite electron-paramagnetic-resonance signal The radiative recombination of electrons with the doubly ionized AsGa double donor is discussed as the origin for the 08 eV band

U. Kaufmann

Papers

Identification of AsGa antisites in plastically deformed GaAs

Rare earth activated luminescence in InP, GaP and GaAs

Annealing Behavior of the 0.8 eV Luminescence in Undoped Semiinsulating GaAs