Observation of indium segregation effects in structural and optical properties of pseudomorphic HEMT structures

Abstract

We present a detailed study on the influence of several growth related factors such as indium segregation, spacer layer thickness and Si δ doping on the structural, optical and electrical properties of molecular beam epitaxy grown pseudomorphic high electron mobility transistor (P-HEMT) structures. Simulation of a high resolution x-ray diffraction (HRXRD) rocking curve was performed and compared with the experimental data to determine the quantum well (QW) thickness and composition as well as the indium segregation related changes in the QW composition. It is shown that growth of a thin layer (6 Å) of GaAs on top of the pseudomorphic InGaAs layer followed by 'flash-off' at a higher temperature could minimize the indium segregation related degradation of the hetero interface. Photoluminescence (PL) and surface photo voltage (SPV) peaks corresponding to the sub-band transitions are analysed using a self-consistent solution of Schrödinger and Poisson equations. PL results showed the dependence of the transition energies on the spacer layer thickness and the effectiveness of the carrier transfer into the InGaAs well. SPV spectra showed characteristic peaks from all the layers in the HEMT structures and were correlated with the data obtained from PL and HRXRD.

The evolution of indium precipitation in gallium focused ion beam prepared samples of InGaAs/InAlAs quantum wells under electron beam irradiation

“…clusters is expected to localise the electrons, and the change of the local density of states(DOS)would degrade the optical properties. [5][6][7] On the practical side, highangle annular dark-field scanning transmission electron microscopy (HAADF-STEM) provides the possibility of observing In segregation or precipitation at the subnanometre scale because HAADF-STEM is very sensitive to changes in average atomic numbers (Z-contrast), which allows the observation of In segregation 8 and compositional variations. 9 In InGaAs/InAlAs quantum wells, due to the large atomic number of In, segregation of In atoms increases the local intensity in HAADF images, which allows a direct mapping of In-rich nanoclusters.…”

“…However, the growth of high In content III–V nitrides quantum wells often suffers from In segregation during growth 1–4 . The formation of In‐rich semiconducting clusters or even metallic In clusters is expected to localise the electrons, and the change of the local density of states(DOS)would degrade the optical properties 5–7 . On the practical side, high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) provides the possibility of observing In segregation or precipitation at the sub‐nanometre scale because HAADF‐STEM is very sensitive to changes in average atomic numbers ( Z ‐contrast), which allows the observation of In segregation 8 and compositional variations 9 .…”

Surface photo-voltage characterization of GaAs/AlGaAs single quantum well laser structures grown by molecular beam epitaxy

“…SPV spectroscopy is a relatively simpler technique, can be done at room temperature and can resolve all transitions in single or multiple quantum wells (MQWs) and superlattices [9][10][11]. We have earlier demonstrated the effectiveness of SPV spectroscopy to characterize pseudomorphic HEMT (high electron mobility transistor) structures consisting of several layers including an InGaAs QW [12].…”