Jeong-Rae Ro

Ga-droplet-induced formation of GaAs nano-islands by chemical beam epitaxy

We report on the fabrication of self-assembled GaAs islands in a nanometer scale by chemical beam epitaxy via Ga droplet formation and subsequent supply of arsine. The density and size of GaAs nano-islands were determined by the nucleation and the growth process of Ga droplets, which were fairly sensitive to the growth condition of Ga droplets, such as the substrate temperature and the amount of TEGa supplied. Transmission electron microscopy observation showed that GaAs nano-islands with well-defined zinc-blende structure were coherently grown on the GaAs surface. Ga droplet-induced formation of GaAs nano-island is thought to be a promising method for fabricating GaAs quantum dots.

Chemical beam epitaxial growth of InGaAs on GaAs(100) using triethylgallium, trimethylindium and unprecracked monoethylarsine

Abstract InGaAs was successfully grown on GaAs(100) substrate by chemical beam epitaxy (CBE) using triethylgallium (TEGa), trimethylindium (TMIn) and unprecracked monoethylarsine (MEAs) as a substitute for arsine. Indium composition of grown layers using unprecracked MEAs is found to be insensitive to the growth temperature of 410 to 590°C unlike that of metalorganic molecular beam epitaxy (MOMBE). Around 460°C, the type conversion of free carrier from n- to p-type was observed as the growth temperature was increased, presumably due to the different bonding energies between GaC and AsC. These results show that the use of unprecracked MEAs in the growth of InGaAs produces a wide growth window for indium composition and low impurity concentrations compared to the use of precracked arsine.

Low carbon incorporation in GaAs grown by chemical beam epitaxy using unprecracked arsine, trimethylgallium and triethylgallium

Abstract GaAs epilayers have been successfully grown by chemical beam epitaxy (CBE) using unprecracked arsine (AsH 3 ) with trimethylgallium (TMG) or triethylgallium (TEG). In the growth using AsH 3 and TMG, three different regions of growth rates were observed with respect to the growth temperature, which is similar to that observed in the conventional CBE or metalorganic molecular beam epitaxy (MOMBE). The growth rates by AsH 3 and TEG, however, produced an anomalous dependence on the growth temperature revealing two humps. Hall measurement, photoluminescence, and secondary ion mass spectrometry (SIMS) analysis data show that all films are p-type and the carbon concentration is greatly reduced compared to the epilayers grown by CBE which employs TMG and precracked arsine. It was also found that the uptake of carbon impurity is significantly reduced when TMG is replaced with TEG. Our results indicate that surface hydrogen atoms dissociated from arsine play an important role in removing hydrocarbon species from the growth surface.

Monoethylarsine as a novel replacement for unprecracked arsine source in the chemical beam epitaxial growth of GaAs using trimethylgallium and triethylgallium

Abstract GaAs epilayers have been succesfully grown by chemical beam epitaxy (CBE) using unprecracked monoethylarsine, which appears to be a viable replacement for arsine in CBE applications. Undoped GaAs epilayers were grown using unprecracked monoethylarsine (MEAs), trimethylgallium (TEG) at growth temperatures of 540 to 660°C, and V/III ratios from 5 to 30. All films grown using TMG under these conditions were p-type. n-Type background doping was also observed in TEG-grown epilayers with low carbon concentration. Secondary ion mass spectrometry and photoluminescence measurements of films grown by MEAs show that the carbon concentration is less than that in epilayers grown by precracked arsine. Intermediates like dihydrides from MEAs decomposed on the surface are considered to supply hydrogen atoms and hydrides during growth, which may remove other carbon containing species.

Selective area epitaxy of GaAs and InGaAs by ultra-high vacuum chemical vapor deposition using triethylgallium, trimethylindium, arsine, and monoethylarsine

We have selectively grown GaAs and InGaAs epilayers on a partially masked GaAs(100) substrate by ultra-high vacuum chemical vapor deposition (UHVCVD) using triethylgallium, trimethylindium, arsine, and monoethylarsine. These results indicate that UHVCVD is a good selective growth method for GaAs and InGaAs in a wide range of growth temperature and V/III ratios. This growth mechanism was also examined using a GaAs(100) substrate patterned with various filling factors (the ratio of the opening area to the total area). These results show that the molecular reactants impinging on the mask are selectively removed from the masked substrate without gas phase diffusion or surface diffusion, resulting in no growth rate enhancement, and in an invariant composition. We also found better selectivity at lower growth temperatures than when metalorganic molecular beam epitaxy/chemical beam epitaxy is used.

Atomic force microscopy study of surface morphology of GaAs grown by atomic layer epitaxy using trimethylgallium and arsine

We have investigated the surface morphologies of GaAs epilayers grown by atomic layer epitaxy (ALE) with atomic force microscopy (AFM) in air. GaAs epitaxial layers were prepared by the ALE technique using trimethylgallium and arsine in an ultrahigh vacuum chemical vapor deposition system. AFM images of ALE epilayers grown at temperatures of 430 and 470 °C showed smooth surfaces with two‐dimensional islands. Furthermore, surface morphology of ALE samples grown at 470 °C was rougher than that at 430 °C presumably due to the desorption of arsenics at higher temperature. These results suggest that the films have been grown in migration‐enhanced epitaxylike mode rather than in an ideal self‐limiting ALE mode.

Size distribution of quantum-scale GaAs islands grown by Ga droplet induced chemical beam epitaxy

We report on the size and the size distribution of GaAs nanoislands via Ga droplet induced chemical beam epitaxy. GaAs nanoislands were grown by the direct injection of triethylgallium and the subsequent supply of thermally cracked arsine on a nonpretreated substrate. The size distribution of islands as measured by the quotient σ/da, the standard deviation of the island diameter (σ) divided by the mean island diameter (da), increases with increasing beam equivalent pressure of triethylgallium but is independent of the total amount of triethylgallium supplied. The influence of annealing was not observed on the size distribution of GaAs islands. These results demonstrate that nanoscale GaAs dots with a narrow size distribution can be achieved by the optimization of growth conditions.

CBE growth of carbon-doped p-type InGaAs using trimethylindium and unprecracked monoethylarsine as carbon auto-doping precursor

Abstract p-type carbon-doped InGaAs on GaAs(100) was successfully grown by chemical beam epitaxy (CBE) using triethylgallium (TEGa), trimethylindium (TMIn), and unprecracked monoethylarsine (MEAs) even though it has been known that p-type conduction can be difficult to obtain when TMIn is used as a carbon auto-doping source. The carrier concentration was strongly affected by growth temperature and TMIn beam flux. The hole concentration decreased with increasing growth temperature and a conductivity inversion from p- to n-type was observed around 450°C. The indium composition of CBE-grown InGaAs using unprecracked MEAs was fairly insensitive to the growth temperatures ranging from 340 to 540°C. The photoluminescence (PL) response in the relaxed InGaAs GaAs layer was not degraded even at the low growth temperature compared to those grown by molecular beam epitaxy (MBE). Our results showed that TMIn and unprecracked MEAs can be used as carbon auto-doping precursors in the CBE growth of p-type InGaAs.

Fabrication of InGaAsGaAs quantum wires on a non-(111) V-grooved GaAs substrate by chemical beam epitaxy

Abstract We have successfully grown InGaAs GaAs quantum wire (QWR) structures on a non-(111) V-grooved GaAs(100) substrate by chemical beam epitaxy (CBE) using triethylgallium, trimethylindium and unprecracked monoethylarsine. To improve the lateral confinement, we have used non-(111) V-grooves which have planes close to (322), where (111) planes are formed near the bottom region during growth, confining QWRs effectively at the bottom of V-grooves. An optimum growth temperature of InGaAs GaAs QWRs was found by examining the temperature-dependent growth rates corresponding to various crystal orientations. Three significant PL peaks were observed at 77 K and related to side QWLs, top QWLs and QWRs with peak energies of 1.439, 1.384 and 1.240 eV, respectively. The luminescence from the QWRs could be still observed even at 200 K. These results suggest that our method using non-(111) V-grooves and unprecracked MEAs is useful method for fabrication of InGaAs GaAs QWRs.

Fabrication of uniform InGaAs/GaAs quantum wires on V-grooved substrate by chemical beam epitaxy

Abstract The stacking of strained InGaAs/GaAs quantum wires was realized by chemical beam epitaxy on V-grooved substrates. In order to stack the uniform InGaAs quantum wires, we have systematically studied the resharpening factor of GaAs barrier layers. The optimal growth condition of GaAs barrier for recovering distorted V-shape was determined to be the use of monoethylarsine as group V source gas at a growth temperature of 450°C. Consequently, we have vertically stacked triple InGaAs quantum wires with an equal size of 300 A ×500 A at the bottom of V-groove. The existence of the quantized state in quantum wires was evidenced by photoluminescence spectra of as-grown and selectively etched samples.