D. Ackley

Coupled‐mode analysis of phase‐locked injection laser arrays

A coupled‐mode analysis has been developed to describe the output of phase‐locked injection laser arrays. We show that an array of emitters with weak coupling can only operate in a set of discrete modes determined by the number and the spacing of the emitters. The interaction between emitters leads to a splitting of the common frequency of operation that can be estimated from the coupling strength. The coupled‐mode analysis is compared to calculations based on simple diffraction theory. A consequence of the analysis is an explanation for the commonly observed discrepancy between experimentally observed far‐field lobe(s) widths and those predicted by simple diffraction theory.

Cyclotron resonance measurements of electron effective mass in strained AlGaAs/InGaAs/GaAs pseudomorphic structures

Electron effective mass in the InxGa1−xAs conduction channel of strained AlGaAs/InGaAs/GaAs pseudomorphic structures is measured using far‐infrared cyclotron resonance techniques at 4.2 K. The measured cyclotron mass is heavier than the conduction‐band‐edge mass in bulk InxGa1−xAs. This result is explained by the large two‐dimensional electron density realized in the structure, and the lattice strain that exists in the InxGa1−xAs layer.

Anomalous dependence of threshold current on stripe width in gain‐guided strained‐layer InGaAs/GaAs quantum well lasers

An anomalous dependence of the threshold current on the stripe width is observed for gain‐guided strained‐layer InGaAs/GaAs quantum well lasers. The threshold current increases strongly as the stripe width is reduced from relatively large values. This is attributed to the huge lateral loss caused by an unusually large index antiguide which manifests itself in the far‐field behavior. This large loss also leads to a population of higher quantized energy levels in the InGaAs quantum well strongly reducing the lasing wavelength by as much as 61 nm.

Conduction‐band offset in strained Al0.15Ga0.85As/In0.15Ga0.85As/GaAs pseudomorphic structures

We report a first determination of the conduction‐band offset in the strained‐layer Al0.15Ga0.85As/In0.15Ga0.85As/GaAs pseudomorphic structure. Two‐dimensional electron density and its effective mass are independently measured by Shubnikov–de Haas and cyclotron resonance experiments for a series of samples with a range of spacer thickness from 30 to 100 A. Using a charge transfer model, the conduction‐band offset at the Al0.15Ga0.85As/In0.15Ga0.85As interface is found to be (255±35) meV.

GaAs light‐emitting diodes with n‐i‐p‐i active layers fabricated by selective contact diffusion

GaAs/AlGaAs light‐emitting diodes (LED’s) with nipi active regions have been successfully fabricated using sequential n and p diffusions to selectively contact the doping superlattice. By doing sequential patterned sulfur and zinc diffusions, a lateral injection LED can be readily fabricated. Excellent current‐voltage characteristics were achieved with reverse breakdown voltages in excess of 9.5 V, indicating that the selective contacts were nearly optimum. cw outputs of 500 μW at 50 mA drive current have been observed. The LED output spectrum was seen to tune with applied bias at a rate of about 650 meV/V at low temperatures.

AlGaAs/GaAs double‐heterojunction high electron mobility transistors grown by low‐pressure organometallic vapor phase epitaxy

AlGaAs/GaAs double‐heterojunction high electron mobility transistors (DHHEMTs) grown by low‐pressure organometallic vapor phase epitaxy are reported in this communication. The magnetic field‐dependent Hall effect measurement was used to characterize the sheet carrier density and electron mobility of the two‐dimensional electron gas (2‐DEG). At 77 K the sheet carrier density and the electron mobility were 1.38×1012 cm−2 and 52 900 cm2 /V s, respectively, in a DHHEMT structure with an undoped Al0.28Ga0.72As spacer layer of 120 A, while they were 7.12×1011 cm−2 and 65 100 cm2 /V s, respectively, in a comparable single‐heterojunction HEMT structure. DHHEMT’s with 0.5‐μm‐gate length and 75‐μm‐gate width have been fabricated with dc saturation current of 500 mA/mm and dc transconductance of 250 mS/mm. These results are comparable to those produced with molecular‐beam epitaxy.

Comparison of RHEED during MBE growth and the quality of AlGaAs:Si grown on (100) and misoriented GaAs substrates

Abstract RHEED surface reconstruction patterns were compared in situ on Si-doped AlGaAs grown side by side on (100) and 6° off toward (111)A GaAs substrates. Different RHEED patterns of AlGaAs were observed under certain growth conditions including the so-called “forbidden range”. Studies of surface morphology and low temperature photoluminesence (PL) indicate that growth on 6° off substrates relaxes the constraints on the growth conditions necessary to obtain high quality AlGaAs between 600 and 680°C.

Excitonic behavior in pseudomorphic InGaAs/(Al,Ga)As quantum wells grown by molecular‐beam epitaxy

Photoluminescence and photoluminescence excitation spectroscopy have been used to study excitons in undoped InGaAs pseudomorphic quantum wells with GaAs and AlGaAs barrier layers. Luminescence features from samples incorporating a top AlGaAs barrier layer were strikingly different from those with bottom AlGaAs barriers. The 2‐K luminescence from the latter structures showed free and bound exciton contributions with a linewidth ≤1.5 meV. In contrast, the luminescence from samples with top AlGaAs barriers was much broader, presumably the result of statistical variations in well width due to island formation at the top interface. Fits to the temperature dependence of the PL linewidth show that while the homogeneous broadening is similar in all the structures, the inhomogeneous broadening introduced by the interfaces is fundamentally different. The results could have important implications for the optimization of heterostructure devices in this pseudomorphic system.

AlGaAs doping superlattices grown by molecular beam epitaxy

AlGaAs dopingsuperlattices (‘‘n i p i structures’’) have been successfully grown in 30% AlGaAs by molecular beam epitaxy. Tunable photoluminescence(PL) as a function of incident laser intensity has been observed in samples with a wide range of intrinsic layer thicknesses over a temperature range from 2 to 120 K. Luminescence shifts as large as 230 meV were observed for a range of incident intensities of about 500. Low‐temperature PL spectra showed a weaker dependence of the peak energy on incident intensity for thicker spacer layers. This decrease in tuning rate can be associated with the reduced probability for tunneling transitions with increasing spacer thickness.