Publications

We discuss revolutionary performance advances in selectively oxidized vertical-cavity surface emitting lasers (VCSELs), which have enabled low operating power laser diodes appropriate for aerospace applications. Incorporating buried oxide layers converted from AlGaAs layers within the laser cavity produces enhanced optical and electrical confinement enabling superior laser performance, such as high efficiency and modulation bandwidth. VCSELs are also shown to be viable over varied environmental conditions such as ambient temperature and ionized radiation. The development of novel VCSEL technologies for advanced system applications is also described. Two-dimensional individually addressable VCSEL arrays exhibit uniform threshold and operating characteristics. Bottom emitting 850 nm VCSEL arrays fabricated using wafer fusion are also reported.

We examine the threshold characteristics of selectively oxidized VCSELs as a function of the number, thickness, and placement of the buried oxide apertures. The threshold current density for small area VCSELs is shown to increase with the number of oxide apertures in the cavity due to increased optical loss, while the threshold current density for broad area VCSELs decreases with increasing number of apertures due to more uniform current injection. Reductions of the threshold gain and optical loss are achieved for small area VCSELs using thin oxide apertures which are displaced longitudinally away from the optical cavity. We show that the optical loss can be sufficiency reduced to allow lasing in VCSELs with aperture area as small as 0.25 micrometer2.

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.

This paper presents the construction of the smart pixel arrays which perform AND and XOR functions with three-input and one-output optical signals for the application of an optical database filter. The device is based on oxide confined VCSELs bump bonded to GaAs MESFET pixels. The MSM photodetectors are monolithically integrated with MESFETs.

To insert high-performance oxide-confined vertical-cavity surface- emitting lasers (VCSELs) into the manufacturing arena, we have examined the critical parameters that must be controlled to establish a repeatable and uniform wet thermal oxidation process for AlGaAs. These parameters include the AlAs mole fraction, sample temperature, carrier gas flow, and bubbler water temperature. Knowledge of these parameters has enable the compilation of oxidation rate data for AlGaAs which exhibits an Arrhenius rate dependence. The compositionally dependent activation energies for Al{sub x}Ga{sub 1-x}As layers of x=1.00, 0.98, and 0.92 are found to be 1.24, 1.75, and 1.88 eV, respectively. 7 figs, 1 tab, 14 refs.

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.

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.

Buried oxides formed from the wet oxidation of AlGaAs alloys, rather than AlAs, are found to be superior in terms of oxidation isotropy, mechanical stability, and strain. It is not surprising that vertical-cavity surface-emitting lasers (VCSELs) using AlGaAs oxide layers as current apertures have shown promising reliability as compared to VCSELs using AlAs layers. Comparisons of lifetime data for VCSELs with differing oxide layers is presented. The beneficial properties of oxides converted from AlGaAs alloys are found to provide robust device processing of reliable VCSELs and may play an important role in other advanced optoelectronic devices.

We report the threshold characteristics of small oxide-confined vertical-cavity surface emitting lasers. Abrupt threshold transitions 105 times the spontaneous emission background are obtained at injection currents as low as 470 nanoampere.

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.

During the past two years significant performance advances have been achieved in selectively oxidized vertical-cavity surface emitting lasers (VCSELs), many of which have established overall benchmark records for semiconductor lasers. These oxidized VCSEL structures leverage the high oxidation selectivity of Al(Ga)As and the capability of forming buried oxide layers within the epilayers of the laser. This paper reviews the advances made in device fabrication, structure and performance of selectively oxidized VCSELs.

We report the effects of mirror doping and reflectivity in 850 and 780 nm oxide-confined vertical cavity surface emitting lasers. Decreased doping throughout the n-type mirror produces significantly higher quantum efficiency, while the optimum reflectivity is dependent upon the gain material.

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.