G. Landgren

1.55 μm buried heterostructure laser via regrowth of semi-insulating InP:Fe around vertical mesas fabricated by reactive ion etching using methane and hydrogen

A GaInAsP/InP Fabry-Perot-type buried-heterostructure quantum well laser operating at 1.55 μm has been realized utilizing iron-doped semi-insulating InP around vertical mesas fabricated by reactive ion etching using methane and hydrogen. A maximum cw output power of 19 mW has been achieved on as-cleaved chips of 300 μm length with a quantum efficiency of 21% per facet. Threshold currents lie between 20 and 25 mA. As low as 2 Ω series resistance has been measured despite an ohmic contact area not exceeding that of the 2-μm-wide mesa. A 3 dB bandwidth of 7.5 GHz at 12 mW output power is obtained from the small-signal frequency modulation measurements.

Importance of metalorganic vapor phase epitaxy growth conditions for the fabrication of GaInAsP strained quantum well lasers

Abstract GaInAsP / GaInAsP multi quantum well (MQW) structures with 1% compressive strain in the wells and a bandgap wavelenght of 1.55 μm have been grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). Photoluminescence (PL) measurements at 300 and 4 K together with X-ray diffraction analysis reveal a strong dependency of the material quality on the MOVPE growth conditions. The photoluminescence intensity could be increased by more than a factor of 3 by optimizing reactor pressure and temperature. Under properly chosen pressure and temperature in the reactor, we found a greatly reduced sensitivity of the material quality to other parameters such as growth interruptions or barrier composition. When utilizing strain-compensating barriers, the number of strained quantum wells could be increased up to 32, without any indication for material degradation due to strain relaxation. Utilizing those findings, distributed feedback (DFB) laser structures employing 8 compressive strained wells with lattice-matched as well as strain-compensating barriers have been grown. The processed lasers showed excellent static and high-frequency characteristics with threshold currents as low as 3.3. mA and a 3dB modulation frequency of 21.7 GHz, which is among the highest values ever reported for DFB lasers.

Diffusion of Zn and Mg in AlGaAs/GaAs structures grown by metalorganic vapor-phase epitaxy

The diffusion of thin, highly p‐doped layers in AlGaAs/GaAs single‐ and double‐heterostructures, grown by metalorganic vapor‐phase epitaxy, was studied with C‐V etch profiling and secondary ion mass spectroscopy. The effect of different post‐growth heat treatments was investigated and diffusion coefficients for both magnesium and zinc were measured. It was found that Mg diffuses about twice as fast Zn and that the order of magnitude of the diffusion coefficient is 10−14 cm2 s−1 at 900 °C, the exact value being process and concentration dependent. A model based on the interstitial–substitutional diffusion mechanism with suitable kinetic limitations was successfully used to simulate the observed dopant concentration profiles.We also found an anomalous strong diffusion of zinc from GaAs into highly n‐doped AlGaAs. Detailed results on this and other structures are presented and implications for optimal design of heterostructure devices such as bipolar transistors are discussed.

Optical bistability and gating in metalorganic vapor phase epitaxy grown GaAs étalons operating in reflection

Nonlinear Fabry–Perot etalons of GaAs have been fabricated with metalorganic vapor phase epitaxy technology. The etalons operate in reflection mode, and have an epitaxially grown, rear dielectric mirror consisting of a stack of alternating AlAs/GaAlAs layers. Optical logic functions using a HeNe laser and optical bistability at room temperature are reported. Low switching powers and improved etalon uniformity are obtained.

Strain variations in InGaAsP/InGaP superlattices studied by scanning probe microscopy

Strain-compensated InGaAsP/InGaP superlattices are studied in cross section by atomic force microscopy and scanning tunneling microscopy. Undulations in the morphology of the {110} cross-sectional faces are observed, and are attributed to elastic relaxation of this surface due to underlying strain arising from thickness and compositional variations of the superlattice layers. Finite element computations are used to extract a quantitative measure of the strain variation.

Interwell carrier transport in InGaAsP multiple quantum well laser structures

We present direct measurements of interwell carrier transport in InGaAsP quantum well (QW) laser structures performed by time‐resolved photoluminescence. Conditions of originally empty and filled wells are explored. In both cases, the time for the hole transport across the structure is found to be of the order of tens of picoseconds. Comparison of experimental results and simulations allowed us to develop an adequate interwell carrier transport model that includes thermionic capture/emission over the QW interfaces and drift/diffusion in the barrier regions. We show that dynamic consideration of carrier densities and band bending for each QW are essential.

Temporally resolved regrowth of InP

Temporally resolved regrowth of InP around reactive ion etched striped mesas without mask is reported. The regrowth was carried out at the growth temperatures of 600, 650, 685 and 700°C in a near equilibrium process, Hydride vapour phase epitaxy (HVPE). The mesa orientations considered were [110] and [110]. The regrowth profiles, initial lateral growth and evolution of certain crystallographic planes are analysed. The regrowth profiles and initial lateral growth rates are dependent on temperature and mesa orientation. The differences are explained by invoking the bonding configurations existing on the mesa walls under the epitaxial growth conditions of excess phosphorus pressure. The facility of lateral growth especially in the [110] mesa case is explained by a more favourable net reduction of dangling bonds. The emerging crystallographic planes are identified as hhl. Initially the planes with lh ≤ 3 are formed but progress towards lh ≥ 3. The implication of a very high lateral growth rate in utilising regrowth for device fabrication is also mentioned.

Influence of MOVPE growth conditions and CCl4 addition on InP crystal shapes

Abstract Growth of InP with metalorganic vapour phase epitaxy (MOVPE) around reactive ion etched stripe mesas has been studied. The mesas were oriented along the [110] and [1 1 0] directions. Marker layers of different doping were introduced in order to follow growth with respect to time. The growth parameters were varied in order to investigate the influence of reactor pressure, V/III ratio, substrate temperature and addition of CCl 4 on the overall growth behaviour. The final crystal shape could, in general, be well described in Wulff diagrams. The results are discussed with respect to diffusion, chemical reactions and surface kinetic aspects. The significant improvement of regrowth properties observed when CCl 4 was added is most probably due to Cl adsorption to group V sites, acting as an inhibitor for P adsorption and hence restricting growth on {111} planes. With CCl 4 present, the reactor pressure and V/III ratio could be used to further control growth on the {111}A and {110} planes. Due to the asymmetry between {110} and {1 1 0} planes, the growth habit was found to be sensitive to the slope of the mesa walls. However, the effect of this sensitivity was diminished when adding Cl.

Topography dependent doping distribution in selectively regrown InP studied by scanning capacitance microscopy

We have used scanning capacitance microscopy (SCM) to study the dopant distribution in regrown InP with high sensitivity and spatial resolution. Sulfur or iron doped InP was selectively regrown around n-doped InP mesas using hydride vapor phase epitaxy, and the resulting structure was imaged in cross section by SCM. For calibration purposes, reference layers with known doping levels were grown directly on top of the region of interest. Dramatic variations in the carrier concentration around the mesa, as well as pronounced differences in the behavior of S and Fe are observed. We correlate these findings to the growth and doping incorporation mechanisms.

Low energy ion beam etching of InP using methane chemistry

Reactive ion beam etching (RIBE) and chemically assisted ion beam etching (CAIBE) of InP at room temperature have been performed, using an inductively coupled plasma source. Two types of chemistries were used: N2/CH4/H2 and Ar/CH4/H2. The etch rate, surface roughness and anisotropy were investigated for different process parameters. In hydrocarbon chemistry polymer buildup is a commonly encountered problem and therefore efforts were also devoted to minimize the polymer growth. Comparing the two chemistries it was found that the Ar based processes always lead to rougher surfaces, while the N2 based chemistry at low ion energies (<100 eV) results in very smooth surfaces for both types of ion beam processes. However, the CAIBE process not only provides smooth surfaces, but also generates much less polymers than its RIBE counterpart. CAIBE, using N2/CH4/H2 chemistry, is then identified as a promising candidate for fabrication of nanometer sized structures. In addition, the low polymer growth is also advantage...