Shigeru Mitsui

Growth temperature dependence in molecular beam epitaxy of gallium arsenide

Abstract Epitaxial layers of GaAs were grown on GaAs(100) at substrate temperatures ranging from 400° to 600°C by molecular beam epitaxy. Surface structures of the substrate and the epitaxial layers were investigated by means of low-energy electron diffraction. Two new structures of c(4 × 4) and c(8 × 8) were observed from layers grown at the low temperature of 400°C. The electrical and optical properties of layers doped with Si were investigated by measurement of Hall effect and photoluminescence as a function of growth temperature. It is found that a semi-insulating layer is grown below a critical temperature, and the layer is useful as a buffer layer for GaAs FETs. Variation of carrier concentration was observed near the interface between layers grown at different temperatures under a constant Sn beam flux. The effect is attributed to defect-induced segregation of Sn.

Thermal stability of AlInAs/GaInAs/InP heterostructures

The origin of the thermal instability of the AlInAs/GaInAs system is identified and a novel method to recover the thermal degradation is also demonstrated. The thermal diffusion of fluorine into the Si‐doped AlInAs layer is found to be the main cause of the electrical deterioration of this system. This finding has led to a method to recover the thermal degradation by purging the fluorine off using the reannealing in the ultrahigh‐vacuum condition. This method is now potentially becoming a good candidate as a tip for the AlInAs/GaInAs devices fabrication including laser diode and high electron mobility transistor.

Overview of recent development of HEMTs in the mm-wave range

Abstract Recent expansion in the demand for high frequency applications requires new transistors with better performance than the MESFETs, especially in the upper-microwave and mm-wave frequency ranges. To realize better transistors than the MESFET by utilizing features of the heterostructure, high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) are being developed. GaAs pseudomorphic HEMTs (PHEMTs) are currently the main type of low noise transistors being used in various microwave and mm-wave systems. Very low noise figures of 1.5 dB at 60 GHz and 2.1 dB at 94 GHz are achieved with GaAs PHEMTs. Furthermore, InP HEMTs, with better noise performance than GaAs PHEMTs, are being developed to replace the latter. State of the art noise figures for InP HEMTs are, for example, 0.8 dB at 60 GHz and 1.2 dB at 94 GHz. GaAs based power HEMTs show higher efficiencies than competing MESFETs for frequencies over 10 GHz, and are comparable to them below 10 GHz. In the higher frequency range, the state of the art in the output power of HEMTs gives a −6 dB/octave line connecting 4W at 20 GHz and 0.1 W at 100 GHz. As there are still reliability problems yet to be solved with the low noise InP HEMTs and the power HEMTs, further study of degradation mechanisms in AlInAs/InGaAs/InP systems, r.f. operation testing of really high power HEMTs, systematic reliable data, etc. would be necessary for them to be accepted as having been established to be reliable devices.

High efficiency thin film silicon solar cells prepared by zone-melting recrystallization

A new type of silicon solar cell is demonstrated using chemical vapor deposited silicon thin films on a silicon dioxide layer. In order to improve the crystal quality of the thin films, zone‐melting recrystallization (ZMR) is applied and grain boundaries of polycrystalline Si films are passivated with H+. It is found that H+ passivation is quite effective for thin film Si solar cells and ZMR conditions to provide dominant (100) orientation is essential for achieving higher conversion efficiency. This (100) nature is also favorable for making effective light confinement scheme with pyramidal textured surface using anisotropic chemical etching. The conversion efficiency as high as 14.2% for a practical size of 10×10 cm2 is achieved. This is the highest for large area thin film polycrystalline Si solar cells so far.

Influence of oxygen on the threshold current of AlGaAs multiple quantum well lasers grown by metalorganic chemical vapor deposition

Abstract The influence of oxygen incorporation into the epitaxial layers on the threshold current density of AlGaAs multiple quantum well (MQW) lasers grown by metalorganic chemical vapor deposition (MOCVD) is studied quantitatively. It is shown that reduction of the oxygen concentration under 1X10 17 cm -3 in the cladding layers is necessary to obtain low threshold current density for the MQW lasers emitting at 780 nm. The effective carrier lifetime measurement in the active layer by time-resolved photoluminescence (PL) spectroscopy is a simple and effective method to monitor the oxygen contamination in the epitaxial layers.

Ultra-high throughput of GaAs and (AlGa)As layers grown by MBE with a specially designed MBE system

Ultra-high throughput MBE growth of very pure and extremely uniform GaAs and (AlGa)As layers with excellent surface morphology can be realized using a newly developed MBE system. High throughput can be achieved by the combination of the simultaneous growth of seven 2 inch or three 3 inch epiwafers and of the automatic growth operated continuously day and night, without accelerating growth rates. The surface defect density has been reduced to the allowable level even for GaAs microwave monolithic ICs. Hall mobilities 1 × 105 cm2/V · s at 77 K were routinely obtained from slightly Si-doped GaAs layers. The microwave devices fabricated from the epiwafers grown by this system showed excellent performance.

High quality Si-doped GaAs layers grown by molecular beam epitaxy

Abstract High quality Si-doped MBE. GaAs layers with high reproducibility have been grown by minimizing the incorporation of impurity species. The electrical and optical properties, and the doping characteristics of the Si-doped layers have been studied, and compared with those of Sn-doped layers. Hall mobility has indicated a low level of compensation in both the Si- and Sn-doped layers. The photoluminescence intensity of the Si-doped layers has been as high as that of the Sn-doped layers. Si-doped layers have shown more abrupt doping profiles than those of the Sn-doped layers, even when the surface segregation effect of the Sn-doped layers has not been observed. The difference in the doping profiles between the Si- and Sn-doped layers is discussed.

Alloyed and Non-Alloyed Ohmic Contacts for AlInAs/ InGaAs High Electron Mobility Transistors

AuGe/Ni/Au alloyed and WSi non-alloyed ohmic contacts are investigated for AlInAs/InGaAs high electron mobility transistors (HEMTs). For the alloyed contact, a contact resistance (R c) lower than 0.03 Ω mm is obtained at an alloy temperature of 300°C. The value of R c drastically increases with alloy temperatures above 300°C and exceeds 0.15 Ω mm at 380°C. Auger analysis and analytical cross-sectional transmission electron microscopy have revealed significant outdiffusion of In in the epitaxial layer into the top Au layer and the formation of polycrystalline GaAs in the epitaxial layer, which cause the increase of R c with alloy temperature. For the refractory WSi non-alloyed ohmic contact, R c remains lower than 0.1 Ω mm under annealing temperatures up to 380°C. The extrinsic maximum transconductance (g m) of 600 mS/mm is obtained for the HEMT device with the WSi ohmic contact.

Photoluminescence Study of Defects in GaAs Formed by Annealing in an H2 Gas Flow

GaAs crystals were annealed in an H2 gas flow and the degraded layer formed on the surface by annealing has been investigated by a photoluminescence measurement. The origin of the defects, in particular an emission at 890 nm, formed by annealing has also been investigated with the aid of the liquid phase epitaxy technique. The degradation of the surface is governed by self-diffusion of As vacancies. The degraded layer depth increases in proportion to the square root of the heating time, whose rate depends on carrier concentrations in the crystals. As the crystals are annealed in an H2 gas flow, new emission band at 890 nm grows drastically. It is concluded that the band is due to electron transitions from a shallow donor to an As vacancy acceptor.

Analysis of the in-plane bandgap distribution in selectively grown InGaAs/InGaAsP multiple quantum well by low pressure metalorganic chemical vapor deposition

Abstract The in-plane distribution of growth rate enhancement and bandgap ( E g ) of the selectively grown InGaAs/In GaAsP multiple quantum well (MQW) structure using a twin stripe mask is investigated. The dependence of the growth rate enhancement and E g transition profile on the mask widthand mask opening width is investigated experimentally, and discussed by the simulation based on the vapor phase diffusion model of the re-evaporated reactant from the mask to the open area. Growth profile in the direction perpendicular to the stripe is explained by one-dimensional vapor phase diffusion. Bandgap transition length along the mask opening stripe decreases with decreasing the mask width and the mask opening width. In-plane bandgap distribution is calculated by simple two-dimensional diffusion model, and the results are consistent with the experimental data.