Gouri Radhakrishnan

Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

We first report on migration‐enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si). Excellent surface morphology GaAs layers were successfully grown on (100)Si substrates misoriented 4° toward the [110] direction. The MEMBE growth method is described, and material properties are compared with those of normal two‐step MBE‐grown or in situ annealed layers. Micrographs of cross‐section view transmission electron microscopy (TEM) and scanning surface electron microscopy (SEM) of MEMBE‐grown GaAs/Si showed dislocation densities of 1×107 cm−2, over ten times lower than those of normal two‐step MBE‐grown or in situ annealed layers. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

Molecular beam epitaxy and metalorganic chemical vapor deposition growth of epitaxial CdTe on (100) GaAs/Si and (111) GaAs/Si substrates

Epitaxial CdTe has been grown on both (100)GaAs/Si and (111)GaAs/Si substrates. A combination of molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has been employed for the first time to achieve this growth: the GaAs layers are grown on Si substrates by MBE and the CdTe film is subsequently deposited on GaAs/Si by MOCVD. The grown layers have been characterized by x‐ray diffraction, scanning electron microscopy, and photoluminescence.

Transient-mode liquid phase epitaxial growth of GaAs on GaAs-coated Si substrates prepared by migration-enhanced molecular beam epitaxy

Abstract Planar oxide-maskless growth of GaAs was demonstrated by transient-mode liquid phase epitaxy (TMLPE) on GaAs-coated Si substrates that were prepared by migration-enhanced molecular beam epitaxy (MEMBE). In TMLPE, the cool substrate was brought into contact with hot melts for a short time. A GaAs layer as thick as 30 μm was grown in 10 s. The etch pits observed in TMLPE-grown layers became longer in one direction and decreased in density with increasing the TMLPE epilayer thickness. The density of etch pits in a 20 μm thick layer was approximately 5 × 10 6 cm -2 . Strong bandgap emission elliptically polarized with a major axis perpendicular to the surface was observed at about 910 nm, while deep-level emission from the TMLPE/MEMBE GaAs interface was detected at 980 nm. The photoluminescence intensity divided by the carrier concentration of the TMLPE-grown layer was about 270 times larger than that of the MEMBE-grown layer used as a substrate.

High‐power low‐threshold graded‐index separate confinement heterostructure AlGaAs single quantum well lasers on Si substrates

A high‐power low‐threshold graded‐index separate confinement heterostructure AlGaAs single quantum well laser on Si substrates has been demonstrated for the first time by a hybrid growth of migration‐enhanced molecular beam epitaxy followed by metalorganic vapor phase epitaxy. The quantum well laser showed an output power of more than 400 mW per facet under pulsed conditions. A room‐temperature threshold current of 300 mA was obtained with a differential quantum efficiency of 40% without facet coating. The threshold current density was 550 A/cm2 for a cavity length of 500 μm. These results show the highest peak power reported to date for low‐threshold lasers on Si substrates. The full width at half maximum of the far‐field pattern parallel to the junction was 6°. Threshold current densities as low as 250 A/cm2 were obtained for lasers on GaAs substrates.

Secondary ion mass spectrometry study of ex situ annealing of epitaxial GaAs grown on Si substrates

Samples of epitaxial GaAs grown on (100) Si substrates using molecular beam epitaxy were annealed at four different temperatures, from 800 to 950 °C. Following annealing, the samples were analyzed using secondary ion mass spectrometry. Depth profiles of Ga, As, and Si reveal optimum conditions for annealing, and place a lower limit on a damage threshold for GaAs/Si substrates.

High-peak-power low-threshold AlGaAs/GaAs stripe laser diodes on Si substrates grown by migration-enhanced molecular beam epitaxy

A high‐peak‐power low‐threshold AlGaAs/GaAs double‐heterostructure stripe laser diode on Si substrates grown by hybrid migration‐enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD) has been demonstrated for the first time. These devices showed the highest peak powers of up to 184 mW per facet reported so far for double‐heterostructure stripe laser diodes on Si substrates, room‐temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30% without mirror facet coating. An intrinsic threshold current density has been estimated to be about 2 kA/cm2 when taking current spreading and lateral diffusion effects into account. Low dislocation density shows that MEMBE can be a useful method to grow high quality GaAs and AlGaAs/GaAs layers on Si substrates by combining with MOCVD.

High-Power AlGaAs/GaAs DH Stripe Laser Diodes on GaAs-on-Si Prepared by Migration-Enhanced Molecular Beam Epitaxy

We report on high-power low-threshold AlGaAs/GaAs double heterostructure (DH) stripe laser diodes on Si substrates by a hybrid growth of migration-enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD). MEMBE-grown GaAs-on-Si had excellent surface morphology and showed much lower dislocation density than that of normal two-step MBE-grown or in situ annealed layers. The MEMBE growth and material characterization are described in detail. The 6-?m-wide oxide stripe lasers showed the highest peak power of up to 184 mW per facet reported to date, room-temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30% without mirror facet coating. The intrinsic threshold current density has been estimated to be about 2 kA/cm2 when taking current spreading and lateral diffusion effects into account. For comparison, the room-temperature pulsed threshold current density of 1.1 kA/cm2 was obtained for the broad-area DH laser diode fabricated on GaAs substrates in the same epitaxial deposition.

Al0.3Ga0.7As/Al0.05Ga0.95As light‐emitting diodes on GaAs‐coated Si substrates grown by liquid phase epitaxy

Al0.3Ga0.7As/Al0.05Ga0.95As double‐heterostructure light‐emitting diodes (LED’s) were successfully grown for the first time by liquid phase epitaxy on a GaAs‐coated Si substrate that was prepared by a sequential process of migration‐enhanced epitaxy and molecular beam epitaxy. The edge‐emitting LED’s had diode ideality factors of 1.54 at a forward‐biased voltage higher than 0.9 V and external quantum efficiencies of 3.3×10−3 W/A per facet. This efficiency is 50 times higher than the previously reported value, and is on the same order as that of AlGaAs homojunction LED’s fabricated on the GaAs substrates by liquid phase epitaxy.

High Peak Power Low Threshold AlGaAs/GaAs Stripe Laser Diodes On Si Substrates By Hybrid MBE/MOCVD Growth

We report high peak power low threshold AlGaAs/GaAs double heterostructure stripe geometry laser diodes on Si substrates grown for the first time by hybrid migration-enhanced MBE (MEMBE) and MOCVD. The lasers with 6 pm silicon oxide stripes were tested unmounted under pulsed conditions (i.e., 50 ns pulse width and 10 KHz pulse repetition rate) at room temperature. These lasers show a peak output power as high as 184 mW per facet and a threshold current as low as 150 mA at 300 K for a cavity length of 350 μm. The differential quantum efficiency of 30 % was obtained without mirror facet coating. A threshold current density of 7 kA/cm2 was obtained based on the nominal stripe dimensions without considering current spreading and lateral diffusion; we estimate about 2 kA/cm2 when taking these effects into account. For comparison, the pulsed threshold current density of the broad area DH lasers on GaAs substrates was 1.1 kA/cm2 at room temperature. This would be further reduced for lasers with a quantum well (e.g., GRIN-SCH SQW) active region. These results show the highest output peak power reported so far with a low threshold current for conventional double heterostructure stripe laser diodes grown on Si substrates.

Growth And Characterization Of CdTe On GaAs/Si Substrates

Epitaxial CdTe has been grown on both (100) GaAs/Si and (111) GaAs/Si substrates. A combination of molecular beam epitaxy and metal organic chemical vapor deposition have been employed to achieve this growth. The GaAs layers are grown on Si substrates by molecular beam epitaxy, followed by the growth of CdTe on GaAs/Si substra by metalorganic chemical vapor deposition. X-ray diffraction, photoluminescence and scanning electron microscopy have been used to characterize the CdTe films.