H. Ohno

Arsenic stabilization of InP substrates for growth of GaxIn1−xAs layers by molecular beam epitaxy

A new method of cleaning InP substrates under molecular beam epitaxy conditions involving heating to ⩾500 °C in an As4 flux (JAs4 ≃1015–1016 cm−2 s−1) is described. Evidence of surface cleanliness, good morphology, ordered surface reconstruction, and integrity of chemical composition at the interface is given. Lattice‐matched layers of Ga0.47In0.53As grown on InP substrates cleaned in this way showed excellent electrical properties: e.g. a room‐temperature mobility μ300=8600 cmPu2 V−1 s−1 at n300 =1016 cm−3.

GaInAs‐AlInAs structures grown by molecular beam epitaxy

Growth of GaInAs and A1InAs by molecular beam epitaxy on idium phosphide substrates is reported. Unintentionally doped, closely lattice matched GaInAs layers were n‐type with μ300 up to 8800 cm2 V−1 s−1 and n as low as 1×1016 cm−3 whereas undoped A1InAs layers were typically high resistance. 2‐MeV Rutherford backscattering showed good GaInAs crystal quality although the A1InAs was somewhat disordered. Evidence for cation exchange at interfaces and surface accumulation of indium was evident from both RBS and sputter Auger profiles. In situ grown A1 films on A1InAs showed an effective barrier height∼0.8 eV from 1/C2 V s V curves, however attention to the forward I‐V characteristics indicated lower values. DLTS results indicate the GaInAs to be virtually trap‐free but that A1InAs has high deep level concentrations owing to low growth temperatures. Good photoluminescent efficiencies were demonstrated for GaInAs layers, however, poor results were obtained for A1InAs.

On the origin and elimination of macroscopic defects in MBE films

Abstract Spitting of group III metal droplets from Knudsen type effusion cells has been found culpable for a genre of problematical macroscopic surface topographical defects observed in the growth of semiconductor films by molecular beam epitaxy. Successful precautions are described which virtually eliminate the problem.

Double heterostructure Ga 0.47 In 0.53 As MESFETs by MBE

Ga<inf>0.47</inf>In<inf>0.53</inf>As MESFETs have been fabricated on InP substrates. The low barrier height of Ga<inf>0.47</inf>In<inf>0.53</inf>As (0.20 eV) which makes simple GaInAs MESFETs at this composition impractical, has been overcome by using thin Al<inf>0.48</inf>In<inf>0.52</inf>As layers between gate metal and GaInAs active layers. Al<inf>0.48</inf>In<inf>0.52</inf>As has also been exploited in the form of buffer layers. The double heterostructure FET wafers with single crystal Al gate metal were grown by molecular beam epitaxy (MBE). The 2.75 µm gate length MESFETs showed d.c. transconductance g<inf>m</inf>= 57 mS mm^-1in spite of nonoptimized dimensions.

On sensor image compression

In this paper, we propose a novel image sensor which compresses image signals on the sensor plane. Since an image signal is compressed on the sensor plane by making use of the parallel nature of image signals, the amount of signal read out from the sensor can be significantly reduced. Thus, the potential applications of the proposed sensor are high pixel rate cameras and processing systems which require very high speed imaging or very high resolution imaging. The very high bandwidth is the fundamental limitation to the feasibility of those high pixel rate sensors and processing systems. Conditional replenishment is employed for the compression algorithm. In each pixel, current pixel value is compared to that in the last replenished frame. The value and the address of the pixel are extracted and coded if the magnitude of the difference is greater than a threshold. Analog circuits have been designed for processing in each pixel. A first prototype of a VLSI chip has been fabricated. Some results of experiments obtained by using the first prototype are shown in this paper.

Integrated double heterostructure Ga 0.47 In 0.53 As photoreceiver with automatic gain control

The first operation of an integrated differential notch-type photoconductor and dual gate (DG) double heterostructure (DH) MESFET in Ga0.47In0.53As is reported. The starting material was grown by molecular beam epitaxy on a semi-insulating InP substrate. A 2 mW HeNe laser with a spot diameter Of 0.5 mm could modulate the drain current by 300 µA with the upper gate suitably biased.

Ultrafast deposition of microcrystalline Si by thermal plasma chemical vapor deposition

This research is an attempt to apply thermal plasma chemical vapor deposition for the ultrafast deposition of Si films for solar cells. The improvement of stability, controllability, and cleanliness of the process enabled the deposition of μc-Si films at the ultrafast rate of over 1000 nm/s. Moreover, a minimum defect density of 7.2×1016 cm−3 was achieved. Monte-Carlo simulation and step coverage analysis suggested that the precursor is an approximately 1 nm cluster with a sticking probability of about 0.6. The success of this research may change the established concepts of Si deposition technology.

Optical quality GaInAs grown by molecular beam epitaxy

Ga47In53As films have been grown by molecular beam epitaxy (MBE) on InP substrates. The unintentionally doped material has a free electron concentration of 8 × 1015cm-3 and exhibits sharp (~5 meV linewidth) exciton recombination in the 4K photoluminescence. The films were grown on (100) InP surfaces which were thermally cleaned in the arsenic beam. The effects of the substrate temperature during growth, the Ga to In flux ratio and the group V to group III flux ratio on the 4K photoluminescence are reported.

Deep level characterization of AlGaAs and selectively doped N‐AlGaAs/GaAs heterojunctions

Deep level characterization of Si‐doped AlGaAs layers and the interface of selectively doped N‐AlGaAs/GaAs heterojunctions grown by MBE is reported. Three electron traps have been detected by DLTS in AlGaAs layers and in N‐AlGaAs/GaAs heterostructures. Two of them are the main dominant levels in the bulk of Si‐doped AlGaAs, which are identified as the well known DX centers. The remaining one shows a peak in concentration near the AlGaAs side of the heterojunction interface in the N‐AlGaAs/GaAs structure and is identified as one of the DX related levels. The effect of these levels on the mobility of electron gas at the N‐AlGaAs/GaAs heterojunction is investigated.

Tangential magnetoresistance of two‐dimensional electron gas at a selectively doped n‐GaAlAs/GaAs heterojunction interface grown by molecular beam epitaxy

Magnetoresistance effect in a two‐dimensional electron gas with high electron mobility (as high as 78 000 cm2/Vs at 77 K) at an n‐GaAlAs/GaAs interface is reported for the magnetic field By, parallel to the interface. This tangential magnetoresistance is shown for the first time to contain a term having a linear dependence both on By and on electric field parallel to the current Ex, and is interpreted in terms of the scattering probability change due to the electron wave function deformation by Lorenz force. The polarity change of the linear term is shown to be the evidence for the one‐sided distribution of ionized impurities.