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We compare a number of strain-sensitive spectroscopic techniques, namely, micro-Raman, micro-photoluminescence, photocurrent, and electroluminescence by applying them to two AlGaAs/ GaAs high-power diode laser arrays, so-called "cm-bars." Both devices are fabricated from the same bar batch and considered "identical," but experienced two different packaging procedures that resulted in different intentionally adjusted "packaging-induced" compressive strains along the array, namely, about -(3.0 ± 0.5) × 10[sup -4] and -(5.0 ± 0.7) × 10[sup -4] strain difference between edges and centers of the bars. The methods are primarily evaluated with respect to their ability to monitor and quantify the different spatial strain distributions along the devices. In addition their potential for defect detection is demonstrated. Pros and cons of the techniques are summarized and discussed. [ABSTRACT FROM AUTHOR]

We investigate optoelectronic properties of monolithically stacked diode lasers, so-called Nanostack® devices that include two nominally identical waveguide segments separated by a specially designed tunnel junction. Near-field optical microscopy provides straightforward and separate access to the properties of both optically active segments. Device emission, namely electroluminescence and lasing, as well as photoluminescence and photocurrent data, are recorded with high spatial resolution and consistently interpreted. We find reduced laser emission from the laser segment that is situated closer to the substrate. We show that this is not caused by thermal effects but most likely due to a larger trap concentration within or in the vicinity of the quantum wells of this laser segment. Furthermore, we show that in the unbiased devices the potential gradient in this segment is significantly larger than in the one close to the heat sink. In addition it is shown that the coupling between both waveguides is marginal. The results underline the potential and unique advantages of near-field optical microscopy for nondestructive analysis of optoelectronic device. [ABSTRACT FROM AUTHOR]

Room-temperature photoluminescence decay time measurements in heavily doped GaAs:C-layers designed as base layers for heterojunction bipolar transistors are reported. These measurements provide access to nonequilibrium minority carrier lifetimes that determine the current gains of those devices. By systematically studying transient luminescence spectra over a wide range of excitation densities between 10[sup 13] and 10[sup 18] cm[sup -3], we demonstrate the importance of carrier trapping processes at low excitation densities. Optimized excitation conditions that achieve trap saturation but also avoid stimulated emission are found for densities of (1–3)×10[sup 17] cm[sup -3]/pulse. Detection is limited to a spectral window well above the energy gap (beyond 1.5 eV). Values for both Auger and radiative recombination coefficients are given. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The transient photoluminescence (PL) from heavily doped GaAs:C study derives reliable room-temperature non-equilibrium carrier lifetime data. The analysis of steady state and transient PL spectra indicates the absence of pronounced not electron effects at room temperature for excitation densities.