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Semiconductor lasers have become the most widely utilized form of coherent light emitters. Aluminum gallium arsenide is the prototype material system in heterostructure laser technology. New fabrication techniques that are simple and easily implemented with present technology may have an impact on laser manufacturing. Hydrogenation is such a process.
Hydrogen compensation of shallow impurities is studied in aluminum gallium arsenide. Data are presented showing the effects of exposure to a hydrogen plasma on n-type GaAs and both n- and p-type Al$\sb{0.75}$Ga$\sb{0.25}$As. Samples are hydrogenated in either a capacitively-coupled or an inductively-coupled rf reactor by placing them on a heated substrate holder (250$\sp\circ$C) within the glow discharge. Carrier concentrations are reduced in the Al$\sb{0.75}$Ga$\sb{0.25}$As, but no compensation is measured in the GaAs sample. The inferred diffusion profile of hydrogen penetrates much deeper in p-type material. This agrees with the proposal that diffusing hydrogen is a deep donor in the crystal. The compensation of acceptors, both Mg and C, in Al$\sb{0.75}$Ga$\sb{0.25}$As can increase the resistivity of the material by 10$\sp5$ after 1 h exposure.
Defining regions of the wafer that are hydrogenated by masking the surface allows fabrication of useful devices with the hydrogenation process. A mask of SiO$\sb2$ or amorphous Si is used to define patterns of conducting stripes separated by regions of highly resistive material. Single-stripe laser diodes reveal that the hydrogenation is a maskable process and achieves effective current confinement down to the active region. Improvements in the as-grown laser heterostructure and the use of carbon as an acceptor allow short plasma exposure times (10 min) for processing. Ten-stripe laser arrays that are fabricated using hydrogenation are capable of generating 0.75 W of optical power. They are phase coupled across the array and have low threshold current densities ($\sim$200 A/cm$\sp2$). Very efficient heat dissipation is achieved, with thermal impedance of 5.6$\sp\circ$/W. Operation in an external grating cavity reveals broadband tunability of these single quantum well ($\sim$140 A) devices and the supermode behavior of the array. Finally, separately-contacted two-stripe laser arrays exhibit strong optical coupling, but nearly complete electrical isolation is achieved by the hydrogenation process. Hydrogenation is a simple, effective process that can be used to create a variety of Al$\sb{\rm x}$Ga$\sb{\rm 1-x}$As-GaAs semiconductor laser devices.
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