R. L. Hartman

The nature and origin of the defects responsible for the rapid degradation of stripe geometry GaAs–GaAlAs double-heterostructure lasers have been identified by transmission electron microscopy. These defects are formed by a three-dimensional dislocation network which originates at a dislocation crossing the GaAlAs and GaAs epilayers. The propagation of the dislocation network takes place by a climb mechanism induced by the operation of the device.

The linear Hall and quadratic magnetoresistance coefficients of bismuth have been measured as functions of temperature in the range 4-16\ifmmode^\circ\else\textdegree\fi{}K. The sensitivity (\ensuremath{\sim}${10}^{\ensuremath{-}12}$V) and accuracy (1 part in ${10}^{4}$) necessary for the experiment required the construction of an automatically balancing superconducting-chopper picovolt potentiometer, together with a cryogenic system which was stable to 1 part in ${10}^{6}$ at any value of temperature in the range 4-16\ifmmode^\circ\else\textdegree\fi{}K. The zero-field resistivities ${{\ensuremath{\rho}}_{11}}^{0}$ and ${{\ensuremath{\rho}}_{33}}^{0}$, normal and parallel to the trigonal direction, respectively, have been measured to 26\ifmmode^\circ\else\textdegree\fi{}K. Both ${{\ensuremath{\rho}}_{33}}^{0}$ and ${{\ensuremath{\rho}}_{11}}^{0}$ are closely proportional to ${T}^{2}$ between 8 and 20\ifmmode^\circ\else\textdegree\fi{}K. All eight magnetoresistance coefficients have an approximate ${T}^{\ensuremath{-}2}$ dependence, while the large Hall term ${\ensuremath{\rho}}_{23,1}$ decreases approximately 7% as the temperature increases from 6 to 16\ifmmode^\circ\else\textdegree\fi{}K. A least-squares fit of the data to a model based on the accepted band structure of bismuth was made at each temperature. From these, experimental values for the carrier density and the components of the mobility tensors for electrons and holes were obtained as a function of temperature. The carrier density, constant with temperature, is 2.7\ifmmode\times\else\texttimes\fi{}${10}^{17}$ electrons per ${\mathrm{cm}}^{3}$, and an equal hole density. All the mobility components varied as ${T}^{\ensuremath{-}2}$ in the temperature range 8-16\ifmmode^\circ\else\textdegree\fi{}K. At 4.2 the electron mobilities are (in ${10}^{7}$ ${\mathrm{cm}}^{2}$/V sec) ${\ensuremath{\mu}}_{1}=11$, ${\ensuremath{\mu}}_{2}=0.3$, ${\ensuremath{\mu}}_{3}=6.7$, ${\ensuremath{\mu}}_{4}=\ensuremath{-}0.71$, ${\ensuremath{\nu}}_{1}=2.2$, and ${\ensuremath{\nu}}_{3}=0.35$. The mobility tilt angle is a constant, ${\ensuremath{\theta}}_{\ensuremath{\mu}}=6.2\ifmmode^\circ\else\textdegree\fi{}$, in the temperature range 4.2-16\ifmmode^\circ\else\textdegree\fi{}K. The components of the conductivity relaxation-time tensor were calculated for the electrons and holes at each temperature. At 4.2\ifmmode^\circ\else\textdegree\fi{}K the maximum anisotropy of the electron relaxation-time tensor was found to be 5:1, decreasing rapidly as the temperature increased, while the anisotropy of the hole tensor was 2:1 over the entire temperature range. At 4.2\ifmmode^\circ\else\textdegree\fi{}K the diagonal components of the electron and hole relaxation-time tensors are (in units of ${10}^{\ensuremath{-}10}$ sec): ${\ensuremath{\tau}}_{1e}=4.4$, ${\ensuremath{\tau}}_{2e}=22$, ${\ensuremath{\tau}}_{3e}=4.4$, ${\ensuremath{\tau}}_{1h}=8.5$, and ${\ensuremath{\tau}}_{3h}=15$. Because the conductivity varies as ${T}^{\ensuremath{-}2}$, we argue that the dominant scattering is not deformation-potential scattering, but rather is between carriers in separate valleys. The carriers in different valleys interact via the Coulomb interaction, each remaining in its respective valley, conserving energy and momentum in the center-of-mass system, though not individually. For carriers of differing charge or of sufficient anisotropy, this mechanism contributes to the resistivity. In support of this mechanism, the electron and hole mobilities at 4.2\ifmmode^\circ\else\textdegree\fi{}K were estimated, from the known ionized-impurity scattering, to be ${\ensuremath{\mu}}_{e}=9\ifmmode\times\else\texttimes\fi{}{10}^{7}$ ${\mathrm{cm}}^{2}$/V sec and ${\ensuremath{\mu}}_{h}=0.6\ifmmode\times\else\texttimes\fi{}{10}^{7}$ ${\mathrm{cm}}^{2}$/V sec, in very good agreement with the measured mobilities.

The rapid degradation phenomenon in Ga1−xAlxAs–GaAs DH lasers has been associated with the growth of a dislocation network during the device operation. The nature of these defects has been analyzed by transmission electron microscopy in an effort to understand their origin and growth mechanism. The propagation of the dislocation network is found to take place by successive climb of a dislocation crossing the n-Ga1−xAlxAs, p-GaAs, and p-Ga1−xAlxAs layers in the stripe area. The climb process leads to the formation of a three-dimensional dislocation dipole network which extends through the three epitaxial layers and remains confined to the stripe area. A tentative model which discusses the network growth process is presented. The source of the very large vacancy concentration involved in the climb process has been attributed to the interfaces between the binary and ternary layers. The fast climb rate has been related to large drift forces acting on the vacancies during the device operation. The dominant drift forces are thought to be electrical and elastic in nature.

Identification of a major failure mechanism in stripe-geometry proton-bombarded double-heterojunction lasers is reported. This mechanism consists of the formation of localized "dark lines" in the optical cavity, coinciding with a decrease in light output. The dark lines are aligned in 〈100〉 crystallographic directions.

Data from accelerated aging tests on continuously operating stripe−geometry double−heterostructure GaAs lasers are presented. By extrapolating data obtained in dry−nitrogen ambients at temperatures of 90, 70, and 50 °C, it is concluded that continuous room−temperature operation of these devices as lasers with power outputs exceeding 1 mW per laser face for times in excess of 100000 h is possible.