A. Yariv

Ultimate limit in low threshold quantum well GaAlAs semiconductor lasers

Gain measurements were performed on buried heterostructure single quantum well lasers to ascertain the transparency current density, which represents a basic limit in the threshold current. By using the optimal design approach, a lowest threshold of 0.55 mA in a 120‐μm‐long device was achieved. Modulation of the low threshold laser by a pseudorandom digital stream at 1.3 Gbit/s without current bias is demonstrated.

The Gaussian Mode in Optical Resonators with a Radial Gain Profile

The dependence of the parameters of the Gaussian mode in laser resonators on the properties of the medium in the cavity is studied. Experimental verification of the theoretical results is presented. It is found that the modes in a high‐gain laser may differ widely from the usual free space resonator results. Also, resonator configurations which in free space are unstable may, with a suitable medium, support low‐loss Gaussian modes.

Dose‐dependent mixing of AlAs‐GaAs superlattices by Si ion implantation

The effects of Si ion implantation and annealing on AlAs‐GaAs superlattices are examined with secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). Samples implanted with 180 keV 28Si+ of doses ranging from 3×1013 to 3×1015 cm−2 are examined before and after a 3‐h 850 °C anneal. Both the TEM and RBS channeling data indicate the formation of a heavily damaged surface layer where diffusion of Al is inhibited even after thermal annealing. After annealing, however, significant mixing is observed at depths well beyond the implant range. Depth‐dependent diffusion lengths of Al and Si are derived from the SIMS data. The diffusion coefficient of Si is markedly reduced in the unmixed regions with both the Si and Al concentrations exhibiting abrupt forward and rear diffusion fronts.

Voltage‐controlled tunable GaAs/AlGaAs multistack quantum well infrared detector

We describe a new type of intersubband GaAs/AlGaAs infrared detector consisting of three stacks of quantum wells; the quantum wells in a given stack are identical, but are different from stack to stack. Each stack is designed to yield an absorption and a photoresponse at a different peak wavelength. The resulting device is an infrared detector which can operate in a number of modes. Among the features of this device are a wide‐band detection domain, a tunable response and excellent responsivities and noise figures. The tunable operation includes a sharp peak‐switching response which follows the formation, expansion, and readjustment of electric field domains within the multiquantum well region.

High-speed digital modulation of ultralow threshold (<1 mA) GaAs single quantum well lasers without bias

GaAlAs buried heterostructure lasers with submilliampere threshold current fabricated from single quantum well wafers can be driven directly with logic level signals without any current bias. The switch‐on delay was measured to be <50 ps and no relaxation oscillation ringing was observed. These lasers permit fully on‐off multigigabit digital switching while at the same time obviating the need for bias monitoring and feedback control.

Effect of substrate tilting on molecular beam epitaxial grown AlGaAs/GaAs lasers having very low threshold current densities

Single quantum well, graded refractive index separate confinement heterostucture (SQW GRINSCH) lasers with well thicknesses in the range of 65–480 A have been grown by molecular beam epitaxy (MBE) on (100) and off of (100) by 4° toward (111) A substrates. The threshold current density appears to be independent of the well thickness in the range of 65–165 A due to the compensating effects of volume of inversion and optical confinement. Under optimum growth conditions, the tilted substrates led to lower threshold current densities, the lowest value being 93 A/cm2 for a 520‐μm‐long cavity laser with a 125‐A‐thick well. To our knowledge, this is by far the best ever reported threshold current density obtained in a semiconductor injection laser. Deviations from optimum growth conditions drastically increased the threshold current density on (100) substrates whereas the degradation for those on the tilted substrates was much less pronounced.

Integration of an injection laser with a Gunn oscillator on a semi‐insulating GaAs substrate

The integration of an injection semiconductor laser with an active electronic device (Gunn oscillator) in a single epitaxial crystal device is demonstrated.

LONGITUDINAL MODES IN A HIGH‐GAIN LASER

In lasers employing high‐gain narrow‐linewidth transitions the theory predicts major departures of the mode‐splitting frequencies from their low‐gain values as well as a new type of mode splitting. The first of these effects consisting of a reduction by a factor of 2.5 of the mode splitting in a xenon 3.51‐μ laser is observed experimentally.

Fundamental mode oscillation of a buried ridge waveguide laser array

An eight‐element phase‐locked array of index‐guided separate confinement ridge AlGaAs diode lasers is fabricated. In this array the absorption of light in the region between lasers is negligible and the gain profile across the array is nearly uniform. Unlike most other arrays, this array oscillates in its fundamental mode. Stable radiation patterns of near diffraction‐limited single narrow beam with 1.6° width are obtained. The beam width approaches the theoretical limit for the present array structure.

Effect of state filling on the modulation response and the threshold current of quantum well lasers

The influence of state filling (carrier population of upper subbands of quantum well laser structures) on the optical gain constant is analyzed in conventional separate confinement quantum well lasers. We find that the appreciable population in the states of the optical confinement layers causes a significant lowering of the differential gain. It is pointed out that strain induced reduction of state‐filling effects is a probable cause of improved performance in the tensile strained quantum well lasers. The strategy of design for very high frequency and very low threshold current quantum well lasers is addressed.