Publications

An electrically injected coupled-resonator vertical-cavity laser (CRVCL) diode is described. The CRVCL consists of a lower 1-λ-thick active resonator containing three InGaAs quantum wells and a passive upper resonator composed of 1-λ-thick GaAs. Some of the characteristics arising from the cavity coupling, including methods for external modulation of the laser are demonstrated.

In this paper the authors report on the direct bonding of compound semiconductors and silicon annealed at low temperatures (400 C) using hydrogen and nitrogen. Pressure and temperature relationships on interface characteristics were investigated with high resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. It was found that no morphology differences existed between hydrogen and nitrogen annealed samples. applying the N{sub 2} bonding process, 850nm bottom emitting vertical cavity surface emitting lasers (VCSELs), were bonded to a transparent AlGaAs substrate. Finally, high anneal temperatures (up to 450 C) and shear stress values (> 1.6 MPa) were obtained for GaAs bonded to Si using a dry (plasma) activation technique.

We discuss the selective conversion of buried layers of AlGaAs to a stable oxide and the implementation of this oxide into high performance vertical-cavity surface emitting lasers (VCSELs). The rate of lateral oxidation is shown to be linear with an Arrhenius temperature dependence. The measured activation energies vary with Al composition, providing a high degree of oxidation selectivity between AlGaAs alloys. Thus buried oxide layers can be selectively fabricated within the VCSEL through small compositional variations in the AlGaAs layers. The oxidation of AlGaAs alloys, as opposed to AlAs, is found to provide robust processing of reliable lasers. The insulating and low refractive index oxide provides enhanced electrical and optical confinement for ultralow threshold currents in oxide-apertured VCSELs.

The differences between buried oxides converted from AlGaAs alloys versus AlAs using selective wet oxidation were reported. The buried oxides formed from the wet oxidation of AlGaAs alloys, rather than AlAs, were found to be superior in terms of oxidation isotropy, mechanical stability, and strain. The vertical cavity surface emitting lasers (VCSELs) using AlGaAs oxide layers as current apertures had shown promising reliability as compared to VCSELs using AlAs layers. Comparisons of lifetime data for VCSELs with differing oxide layers are presented. The beneficial properties of oxides converted from AlGaAs alloys were found to provide robust device processing of reliable VCSELs and may play an important role in other advanced optoelectronic devices.

An accurate first-principles analysis to probe the threshold properties of selectively oxidized vertical-cavity surface-emitting lasers (VCSELs) were developed. The analysis indicates that in order to achieve ultralow threshold, oxide aperture scattering loss and leakage currents must be addressed. The agreement between calculations and experiment solidify the understanding and enable the identification of fundamental limitations of low threshold VCSEL operation. The performance and analysis of modified VCSEL designs are presented.

Metallorganic chemical vapor deposition (MOCVD) technology is increasingly recognised as a superior platform for growth of vertical-cavity surface-emitting lasers (VCELs) because of its high throughput, low surface defect density, continuous compositional grading control, and the flexibility for materials and dopant choices. In this paper, it is shown that it is also capable of extremely high wafer uniformity and run-to-run reproducibility.

A systematic study has been carried out on the effects of doping concentration and reflectivity of the mirror and the oxidation fabrication on the efficiency of 850- and 780-nm oxide-confined VCELs. By optimizing the mirror-doping profile and reflectivity, hex > 40-50% have been achieved. Furthermore, the oxidation temperature can directly influence the VCFL performance. Finally, additional optimization studies and the implementation of the results in optimal VCFL structures have been described.

The gain-dependent polarization properties of vertical-cavity surface emitting lasers and methods for polarization control and modulation are discussed. The partitioning of power between the two orthogonal eigen polarizations is shown to depend upon the relative spectral alignment of the nondegenerate polarization cavity resonances with the laser gain spectrum. A dominant polarization can thus be maintained by employing a blue-shifted offset of the peak laser gain relative to the cavity resonance wavelength. Alternatively, the polarization can be controlled through use of anisotropic transverse cavity geometries. The orthogonal eigen polarizations are also shown to enable polarization modulation. By exploiting polarization switching transitions in cruciform lasers, polarization modulation of the fundamental mode up to 50 MHz is demonstrated. At lower modulation frequencies, complementary digital polarized output or frequency doubling of the polarized output is obtained. Control and manipulation of vertical-cavity laser polarization may prove valuable for present and future applications.