Search

In this work, we show how diffraction-based chemically sensitive dark-field transmission electron microscopy (DFTEM) reveals the presence of Bi hetero-antisites (BiGa) at the interface of Ga(As,Bi)/(Al,Ga)As quantum well (QW) structures grown by molecular beam epitaxy on GaAs(001). The presence of BiGa is demonstrated by the striking appearance of "dark-lines" at the interfaces under two-beam DFTEM imaging conditions using the (002) diffraction spot. Additional analytical scanning (S)TEM procedures reveal Ga depletion and Bi accumulation at the exact position of the dark-lines, consistent with BiGa at this location. The precise location of the dark-lines agrees with the position of growth interruptions made to adjust substrate temperature and the As/Ga flux ratio and, most importantly, the realization of a Bi pre-treatment before QW growth. We believe the Bi pre-treatment may have favored formation of BiGa hetero-antisites. We validate the use of g002 DFTEM for further investigations of the intricate bismuth incorporation into the lattice and its dependence on the growth conditions. Finally, g002 DFTEM imaging is positioned as a very powerful technique for the detection of point defects in general in materials with the zinc-blende crystal structure, beyond dilute bismide alloys. [ABSTRACT FROM AUTHOR]

The drift velocity (vdrift) of electrons in an n‐type modulation‐doped GaAs0.96Bi0.04/Al0.15Ga0.85As quantum well (QW) structure is determined for electric fields (F) ranging from ≈0.4 to 3.58 kV cm−1. The resulting vdrift characteristic exhibited a linear increase and reached ≈6 × 106 cm s−1 at low electric fields then almost saturated with increasing electric field. The electron drift mobility is determined as 2265 cm2 Vs−1 in the regime where the drift velocity is linear with respect to the electric field. The drift velocity saturates at ≈6.1 × 106 cm s−1 at the electric fields between ≈2.7 and 3.4 kV cm−1. Saturation of the drift velocity is attributed to the transfer of the electrons from the QW layer (GaAs0.96Bi0.04) with higher electron mobility to the barrier layer (Al0.15Ga0.85As) and satellite valley L‐valley with lower electron mobility, which initiates cooling of electrons via phonon scattering in the sample. [ABSTRACT FROM AUTHOR]

We report the first (to our knowledge) wafer-fused high-power passively mode-locked semiconductor disk laser operating at 1.57 microm wavelength. An InP-based active medium was fused with GaAs/AlGaAs distributed Bragg reflector on a 2 inch wafer level, resulting in an integrated monolithic gain mirror. An intracavity wedged diamond heat-spreader capillary bonded to the gain chip provides efficient heat removal from the gain structure without disturbing the spectrum of the mode-locked laser. The laser produces over 0.6 W of average output power at 15 degrees C with 16 ps pulse width. The total output power accounting for all output beams emerging from the cavity was 0.86 W. The results reveal an essential advantage of wafer fusion processing of disparate materials over monolithically grown InP-based gain structures and demonstrate the high potential of this technique for power scaling of long-wavelength semiconductor disk lasers.