Tae-Wan Lee

Effects of As/P exchange reaction on the formation of InAs/InP quantum dots

InAs self-assembled quantum dots (SAQDs) were grown on InP at various temperatures and V/III ratios by metalorganic chemical vapor deposition. The density, size distribution, and shape of the InAs SAQDs changed significantly with temperature and V/III ratio. Careful analysis of the total volume of the dots grown at various conditions showed that the volume far exceeded the amount of deposition supplied from the gas-phase sources. The amount of excess InAs and the aspect ratio (height/lateral size) of the SAQD increased with temperature and V/III ratio, strongly suggesting that the As/P exchange reaction at the surface played an important role in the kinetics of SAQD formation. Insertion of a lattice-matched InGaAs buffer layer suppressed the excess InAs formation, and lowered the aspect ratio, confirming the effect of the As/P exchange reaction.

Shape change of InAs self-assembled quantum dots induced by As/P exchange reaction

Abstract Self-assembled InAs quantum dots (SAQDs) were grown on InP and on lattice-matched InGaAs buffer layers by metalorganic chemical vapor deposition (MOCVD). The aspect ratio of the SAQD grown on InP increased with temperature and V/III ratio, but it reduced substantially when grown on InGaAs buffer layers. Moreover, the dots formed on InGaAs were faceted, whereas those on InP were dome-shaped, strongly suggesting that the As/P exchange reaction at the surface played an important role in the kinetics of SAQD formation. The shape of InAs SAQDs on InGaAs buffer layers was a truncated pyramid with four {136} facets and their base edges were parallel to 〈130〉 directions.

Analysis of P adsorption and desorption on the (001) InP surface using surface photoabsorption

We present an in situ study of P desorption and adsorption on the (001) InP surface using surface photoabsorption (SPA). The SPA spectra show three peaks at 2.1, 2.9, and 3.1 eV. Here, based on previous studies, we have identified them as a P dimer related and two surface In dimer related peaks, respectively. The initial sharp drop and the slow recovery of the SPA signal at 430 nm after PH3 is switched on implies that at least two steps are involved in the P desorption process. We also observed a structure at 3.1 eV in the spectrum of the In-stabilized surface. We have determined from temperature dependent desorption measurements that the activation energy for P desorption from this surface is 3.36 eV.

Observation of two independent sources for arsenic carryover

Abstract The two independent As carryover processes were observed by photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) from the same InAs x P 1− x /InP single quantum well (SQW) samples formed after AsH 3 exposure. The combination of the SQW with a very thin InP capping layer enabled us to observe by HRXRD the weak modulation peaks from the InP buffer layer, where a minute amount of As was incorporated due to the As carryover from the interior of the reactor. Simultaneously the PL peak energies blue-shifted with AsH 3 treatment temperature due to the excess As adsorbed on the InP surface. These results clearly show that the As carryover from two sources occurs independently, and simultaneously.

In situ analysis of surface photoabsorption spectra during InP ALE in metal organic chemical vapor deposition

Abstract In situ monitoring of InP atomic layer epitaxy (ALE) by surface photoabsorption (SPA) was performed in low-pressure metal organic chemical vapor deposition. Self-limiting adsorption condition of In species was studied for various TMIn injection times. A grazing incidence X-ray study on the thickness of the film grown by ALE, however, showed that the growth rate did not reach one monolayer (ML)/cycle. The SPA signal trace measured during the InP ALE indicated incomplete PH 3 decomposition on the methyl-terminated In surface, and this observation was attributed to the cause of submonolayer growth. We also report a spectroscopic SPA study on the surface state during a cycle of ALE process. The SPA spectrum of the methyl-terminated In surface showed a different line shape at around 1.9 eV (In-dimer region) from that of an In-stabilized surface. But, during H 2 purge at 390°C, this portion of the spectrum was observed to evolve to that of an In-stabilized surface by the desorption of methyl radical.

Possibility of Two-Step As-Desorption from (001) InP Using Surface Photoabsorption

We present an in situ investigation of As-desorption from the (001) InP surface using surface photoabsorption (SPA). At 470°C, we observed that the SPA signals along [110] remained unchanged even after the AsH3 supply was turned off, while the SPA signal along [110] showed a sharp increase as reported previously. We also measured SPA spectra at several stable states and found that the surface after AsH3 was turned off could not reach that of an In-stabilized surface. We interpret these results in terms of As-desorption occurring possibily as a two-step process, in contrast to P-desorption of a one step process.

Analysis of Surface Photoabsorption Spectra of (001) InP Surfaces

We present an in situ surface photoabsorption (SPA) study on surface structures of (001) InP surfaces. Conventional subtraction spectra of SPA on (001) InP showed two peaks at 430 nm and 600 nm, which we assigned as P dimer and In dimer peaks, respectively. By modifying the conventional subtraction equation to separate contributions from In- and P-stabilized surfaces, we could observe another structure at 400 nm which we interpret as related to In-stabilized surface, showing possibility of complementary role of this modified equation. We also observed evolution of surface states from P- to In-stabilized surfaces at 600°C by the change of PH3 partial pressure.

Asymmetric growth behavior of selectively grown InP on vicinal (1 0 0) surfaces by low-pressure metal-organic chemical vapor deposition

Abstract Shape changes in selectively grown InP mesas were studied at various wafer-tilting and stripe misalignment angles by low-pressure metal-organic chemical vapor deposition. Symmetric mesa structures were obtained irrespective of stripe misalignment when the wafers were not titled. However, asymmetric ear formation was observed when the wafers were tilted and stripes were misaligned. A model for the changes in step density with wafer tilting and stripe misalignment was proposed to explain the asymmetric ear formation. The effect of V III ratio on the asymmetric ear formation was also studied.

Observation of As carryover from two different As sources

The As carryover processes from two different As sources were observed simultaneously but separately by photoluminescence (PL) and high resolution x-ray diffraction (HRXRD) in InAs/sub x/P/sub 1-x//InP single quantum wells (SQWs) formed by AsH/sub 3/ exposure. One of the main As source of carryover, As absorbed on the epilayer surface, was observed by PL as a blue shift of peak energy with growth temperature. The other source, re-evaporated As from the interior of the reactor, was also detected in the same samples by an abnormal HRXRD rocking curve, and the concentration of As in the buffer layer was quite uniform though its amount was minute. Finally, it was briefly considered that how the two carryover processes were observed simultaneously, especially in this study.

In-situ observation of As/P exchange reaction and As carryover in InAs/InP quantum well structures by surface photoabsorption

InAs/InP quantum well structures were grown by low pressure metal organic chemical vapor deposition. During the growth, the As/P exchange reaction and As carryover were monitored in-situ by surface photoabsorption. We simulated the measured SPA signal using a multilayer model and effective medium theory to obtain the As compositional profile which was carried over into the InP layer.