Hal A. Zarem

Direct determination of the ambipolar diffusion length in GaAs/AlGaAs heterostructures by cathodoluminescence

A new technique for determining carrier diffusion lengths by cathodoluminescence measurements is presented. The technique is extremely accurate and can be applied to a variety of structures. Ambipolar diffusion lengths are determined for GaAs quantum well material, bulk GaAs, Al0.21Ga0.79As, and Al0.37Ga0.63As. A large increase in the diffusion length is found for Al0.37Ga0.63As and is attributed to an order of magnitude increase in lifetime.

Gain spectra of quantum wires with inhomogeneous broadening

The effects of fabricational variations on the gain spectra of quantum wires are calculated within the limits of first-order perturbation theory. Gain spectra and density of states for 50-AA-radius and 150-AA-radius cylindrical quantum wires are calculated and plotted for several different fabrication tolerances. The wave functions for a finite, cylindrical potential are calculated and a quasicritical radius, below which the carriers are weakly confined by the potential, is established. This sets a lower limit on quantum wire size. Upper limits on the size of quantum wells, quantum wires, and quantum boxes are also discussed. The threshold current and differential gain of quantum-wire lasers and quantum wire array lasers are calculated. These calculations indicate a possible reduction in threshold current of one to two orders of magnitude as compared to the best quantum-well lasers. >

Passive mode locking of a two‐section multiple quantum well laser at harmonics of the cavity round‐trip frequency

A multiple quantum well GaAs/AlGaAs laser with two electrically isolated contacts is passively mode locked in an external cavity at the first through sixth harmonics of the pulse round‐trip frequency of 1.17 GHz to produce pulses shorter than 10 ps. The repetition rate is switched between harmonics by adjusting the gain section current, and large hysteresis between the different repetition rates is observed, with up to four different repetition rates for the same gain current. The results are compared with small and large signal passive mode‐locking theories by considering modifications to the saturated gain recovery between pulses when the laser operates at different harmonics.

Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1−xAs

The ambipolar diffusion length and carrier lifetime are measured in AlxGa1−xAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented.

An experimental and theoretical study of the suppression of interferometric noise and distortion in AM optical links by phase dither

The effects of phase dither on the magnitude and spectral distribution of interferometric fiber optic noise and intermodulation products is considered. A theory is presented as well as experimental data which show major reduction of AM noise brought about by intentional narrow band and wide band phase dither of the laser output.

Timing jitter and pulse energy fluctuations in a passively mode‐locked two‐section quantum‐well laser coupled to an external cavity

Stability of pulse energy and timing in a passively mode‐locked two‐section quantum‐well laser is measured. Spectral analysis of the 546‐MHz pulse train reveals rms timing jitter of 5.5 ps above 50 Hz and rms pulse energy fluctuations of <0.52% above 200 Hz.

Nanometer scale wire structures fabricated by diffusion‐induced selective disordering of a GaAs(AlGaAs) quantum well

A shallow zinc diffusion technique is used to selectively disorder a GaAs quantum well creating nanometer scale wire structures. Spectrally resolved cathodoluminescence images of the structures are presented as well as local spectra of cathodoluminescence emission from the structures. Blue shifting of the luminescence from the wire structures is observed.

High-power single mode strained-layer lasers emitting at 980 nm

Highpower single mode InGaAs lasers for emitting at 980mn have been developed. Life test data and failure analysis results are discussed. Coupling efficiency into single mode fiber as a function of beam ellipticity is also studied.

A novel technique for the direct determination of carrier diffusion lengths in GaAs/AlGaAs heterostructures using cathodoluminescence

A novel technique for determining carrier diffusion lengths in direct gap semiconductors by cathodoluminescence measurement is presented. Ambipolar diffusion lengths are determined for GaAs quantum-well material, bulk GaAs, and Al/sub x/Ga/sub 1-x/As with x up to 0.38. A large increase in the diffusion length is found as x approaches 0.38 and is attributed to an order-of-magnitude increase in lifetime.<<ETX>>

Quantum wire and quantum dot semiconductor lasers

There is currently great interest in fabrication of structures that are two and three dimensional analogs of the conventional quantum well. We review here the physics behind the use of arrays of such lower dimensional structures in semiconductor laser active layers. Methods which are currently under investigation for producing such structures will be discussed.