Ion implantation for isolation of III-V semiconductors

This review covers a spectrum of optoelectronic properties of and uses for semi-insulating semiconductor heterostructures and thin films, including epilayers and quantum wells. Compensation by doping, implantation, and nonstoichiometric growth are described in terms of the properties of point defects and Fermi level stabilization and pinning. The principal optical and optoelectronic properties of semi-insulating epilayers and heterostructures, such as excitonic electroabsorption of quantum-confined excitons, are described, in addition to optical absorption by metallic or semimetallic precipitates in these layers. Low-temperature grown quantum wells that have an arsenic-rich nonstoichiometry and a supersaturated concentration of grown-in vacancies are discussed. These heterostructures experience transient enhanced diffusion and superlattice disordering. The review discusses the performance of optoelectronic heterostructures and microcavities that contain semi-insulating layers, such as buried heterostructure stripe lasers, vertical cavity surface emitting lasers, and optical electroabsorption modulators. Short time-scale applications arise from the ultrashort carrier lifetimes in semi-insulating materials, such as in photoconductors for terahertz generation, and in saturable absorbers for mode-locking solid state lasers. This review also comprehensively describes the properties and applications of photorefractive heterostructures. The low dark-carrier concentrations of semi-insulating heterostructures make these materials highly sensitive as dynamic holographic thin films that are useful for adaptive optics applications. The high mobilities of free carriers in photorefractive heterostructures produce fast dielectric relaxation rates that allow light-induced space-charge gratings to adapt to rapidly varying optical fringe patterns, canceling out environmental noise during interferometric detection in laser-based ultrasound, and in optical coherence tomography. They are also the functional layers in high-sensitivity dynamic holographic materials that replace static holograms in Fourier imaging systems and in experimental Tbit/s optical systems. Semi-insulating heterostructures and their applications have attained a degree of maturity, but many critical materials science issues remain unexplored.

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Semi-insulating semiconductor heterostructures: Optoelectronic properties and applications

On the electrical properties of compound semiconductor interfaces in metal/insulator/ semiconductor structures and the possible origin of interface states

We investigate the origins of mode confinement, parallel to the junction plane, of stripe‐geometry double‐heterostructure GaAs injection lasers. Based upon the kind of control of the mode extent by the stripe width, we establish a distinction between two types of lasing mode guidance; (i) well‐behaved, where a single mode substantially fills the entire active region, and (ii) filamentary, where the mode size is much smaller than the width of the active region and its location is random. For low‐order well‐behaved modes, it is shown, at least in principle, that gain alone (no refractive index effects are required) can explain not only the confinement but also the approximate waveguide dimensions for which leakage losses, connected with the penetration of the mode into the regions outside the active guide, become important. When only this postulated gain‐guiding prevails in the case of higher‐order modes, we find that their spatial character is markedly different from the Hermite‐Gaussian distributions which have been seen for GaAs lasers. The introduction of a positive incremental index, which may reasonably be associated with the gain and/or with a thermal mechanism, restores agreement with observation. If any incremental index within the active region is negative, then although there is a defocusing effect, confinement may still be maintained by the gain. In the case of filamentary lasing we analyze four focusing mechanisms; two are connected with local built‐in gain (loss) and refractive index variations, while two are current dependent and are related to the saturation of gain‐associated refractive index and the free carrier effect. While all four processes appear to be reasonable candidates for providing the necessary confinement in filamentary lasing, the latter two simultaneously violate a condition necessary for stability of a filament. We conclude that imperfections in lasers are likely to be related to filamentary lasing and that such behavior may not be intrinsic to such devices.

Mode guidance parallel to the junction plane of double-heterostructure GaAs lasers

A method of defining the active region of stripe-geometry junction lasers by proton-bombardment-induced high-resistivity layers is described. The method yields more reproducible mode patterns and lower threshold currents than the previously used oxide insulation. The improved lasers operated continuously at heat-sink temperatures up to 110°C.

Proton-bombardment formation of stripe-geometry heterostructure lasers for 300 K CW operation

The effect of 300‐keV proton bombardment and subsequent annealing on the optical absorption and electrical resistivity of bulk p‐type (p=2×1018 and 1.4×1019 cm−3) GaAs has been studied. Proton doses were in the range 1013−1017 cm−2. It is found that bombardment‐induced optical absorption increases monotonically, but sublinearly, with proton dose. The shape of the optical transmission spectrum indicates that bombardment creates a distribution of energy levels extending into the forbidden gap. Activation energies for annealing of the optical absorption have been determined from isothermal annealing data and range from ∼1.5 to ∼3.4 eV, which indicates that at least two kinds of defects are involved. Current‐voltage measurements show that the average electrical resistivity of the bombarded layers goes through a maximum at ∼2.5×105 Ω cm at a proton dose of ∼3×1015 cm−2. It is shown that annealing can eliminate the bombardment‐induced optical absorption while still retaining a high electrical resistivity. The o...

Optical and electrical properties of proton‐bombarded p‐type GaAs

A proton-bombardment method of preparing stripe geometry junction lasers is reported here, and the operating characteristics of these new devices are compared with the previously described oxide-insulated stripe geometry lasers. In a typical procedure, a slice containing an epitaxially grown heterostructure is bombarded with protons producing a high-resistivity layer 3 µm deep which penetrates through the active p-region of the device. The lasing region is masked from the protons by evaporated and photo-etched gold stripes 3µm thick. The device is then annealed at 450°C for 15 min. to remove the undesired bombardment-induced optical absorption while still retaining sufficiently high resistivity for current confinement. For a 12 µm wide strip, the resulting double heterostructure lasers have room temperature threshold currents which are typically a factor of two lower than the oxide-insulated lasers. Bombardment-insulated lasers have operated continuously on diamond heat sinks up to 110°C (heat sink temperature), often in the lowest order spatial mode. There appear to be no aging effects whicll can be attributed to bombardment.

J. C. Dyment

Papers

Optical and electrical properties of proton‐bombarded p‐type GaAs

Proton bombardment formation of stripe-geometry heterostructure lasers for 300°K CW operation

J. C. Dyment

Papers

Optical and electrical properties of proton‐bombarded p‐type GaAs

Proton bombardment formation of stripe-geometry heterostructure lasers for 300&#176;K CW operation

Proton bombardment formation of stripe-geometry heterostructure lasers for 300°K CW operation