Thick GaAs Buffer Layer Research Articles

Enhancement of compositional disordering in strained [formula omitted] quantum wells by Zn diffusion

We report the enhancement of InGa interdiffusion in strained In x Ga 1− x As GaAs (x=0.20–0.24) single quantum well (QW) structures by surface Zn diffusion. The epitaxial structures were grown by MOVPE and consist of a 1–2μm thick GaAs buffer layer, followed by the In xGa 1−xAs QW with 80–100Å thickness and a GaAs cap layer 500–1000Å thick. We have performed various shallow Zn diffusion depths for times and temperatures ranging from 1.3 to 3.5min. and 585–620°C, respectively, in order to vary the Zn concentration in the QWs. The samples were then annealed between 650–785°C under AsH 3 H 2 to determine the enhanced InGa interdiffusion coefficient and its activation energy. A model is proposed to explain the enhancement of interdiffusion by Zn diffusion which involves an interstitial migration process.

Heteroepitaxial growth of InP on Si substrates

Heteroepitaxy of a highly mismatch system (∼8%), InP/Si has been studied using low pressure organometallic vapor phase epitaxy (OMVPE). Buffer layer effects on residual stress and defect density in InP/Si have been clarified. Using a 1 μm thick GaAs buffer layer, residual stress in the InP layer has been reduced to as low as 2×10 8 dyn/cm 2 compared to ∼4×10 8 dyn/cm 2 for InP directly grown on Si and ∼6×10 8 dyn/cm 2 for InP on Si with a 1 μm thick GaP buffer layer. Moreover, the GaAs buffer layer has also been confirmed to be effective for improving InP/Si quality by evaluation of etch-it density, X-ray diffraction measurement and observation of cross-sectional transmission electron microscopy. For an InP/GaAs/Si structure, InP growth temperature dependence on surface morphology and etch-pit density is also shown. High quality InP films with etch-pit density of 8×10 6 cm -2 has been obtained on Si substrates by using thermal cycle growth and an InP/GaAs/Si structure.

MBE Grown GaAs on Si(100) Studied by Infrared Spectroscopy

AbstractGaAs layers were deposited onto Si(100) substrates using molecular beam epitaxy (MBE). The substrates were prepared by various methods before the growth of 0.1µm thick GaAs buffer layers. Active GaAs layers were thereafter grown with thicknesses from 1 to 4µm. Infrared spectra were recorded in the spectral ranges from 12 to 65cm-4 and 50 to 500cm-1 of the thin buffer layers as well as the thick active layers. The infrared active phonon of GaAs already shows up in the spectra for the 0.1µm buffer layers. The phonon parameters were derived from a harmonic oscillator fit to the experimental data. The phonon damping constant is correlated with the bulk quality of the GaAs layers. These results are compared with those obtained from Raman and spectroscopic ellipsometry measurements.

The dependence of AlGaAs/GaAs MODFET isolation on material and device structure

Investigations on the dependence of AlGaAs/GaAs Modulation Doped Field Effect Transistor (MODFET) isolation on device and epitaxial material structure are reported. For single heterojunction devices with thick (1 μm) undoped GaAs buffer layers, the backgating characteristics are found to be independent of device structure and backgate-MODFET spacing. In the case of thin GaAs buffer layer structures ( ⩽2000 A ̊ ), a considerable backgating dependence on device structure is observed. For a 2000 Å buffer layer and a particular device structure, the drain-source current is found to drop by only ∼ 3% when −10 V is applied to a backgate contact located 2 μm from the MODFET. The excellent isolation provided by this device and material structure is attractive for fabrication of high packing density integrated circuits with reduced material growth times.

Photoconductivity in selectively n- and p-doped Al xGa 1− xAs/GaAs heterostructures

The doping characteristics of direct-gap bulk n-Al x Ga 1− x As doped with Si and grown by molecular-beam epitaxy are determined by the coexistence of shallow and deep donors, both of which are caused by Si-impurities. The deep donor is ionized thermally at high temperatures and optically at low temperatures, resulting in a persistent increase of the free carrier concentration. The persistent photoconductivity in selectively n-doped n-Al x Ga 1− x As/GaAs heterostructures is predominantly caused by the photoionization of the deep Si-donor in the Al x Ga 1− x As layer. Electron-hole generation in the GaAs contributes only a minor part to persistent photoconductivity in n-type heterostructures. In p-type heterostructures, however, electron-hole generation is the dominant mechanism responsible for persistent photoconductivity and contributes 5 × 10 10 holes per cm 2 for a 1 μm thick GaAs buffer layer to the two-dimensional electron- (hole-) gas. The hole concentration in selectively p-type heterostructures is calculated versus (i) Al-mole fraction, (ii) acceptor concentration in the p-Al x Ga 1− x As, and (iii) Al x Ga 1− x As spacer width. Theoretical hole concentrations agree well with experimental data, if the bandgap difference of GaAs and Al x Ga 1− x As is taken to be distributed by a ratio of if 75 25 to the conduction- and valence-band discontinuity. Hall measurements on selectively p-doped Al x Ga 1− x As/GaAs heterostructures reveal a freeze-out of carriers and high hole mobilities at low temperatures. The acceptor binding energy in the p = Al x Ga 1− x As:Be is determined to be E a = 26 ± 3 meV for x = 0.45.