J. Barnard

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.

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.

Double heterostructure Ga 0.47 In 0.53 As MESFETs with submicron gates

MESFETs with GA<inf>0.47</inf>In<inf>0.53</inf>As active channel grown by MBE on InP substrates were successfully fabricated. Thin layers of MBE grown Al<inf>0.48</inf>In<inf>0.52</inf>As seperated both the single crystal aluminum gate from the active channel and the active channel from the InP substrate so raising the Schottky barrier height of the gate and confining the electrons to the channel. The MESFETs with 0.6µm long gates and gate-to-source separations of 0.8 um exhibited an average g<inf>m</inf>of 135 mS mm^-1of gate width for V<inf>ds</inf>= 2V and V<inf>g</inf>= 0. This is higher than that reported for GaAs MESFETs with a similar geometry in spite of the intermediate layer between the gate metal and the active layer.

Preparation and properties of molecular beam epitaxy grown (Al 0.5 Ga 0.5 ) 0.48 In 0.52 As

The first reported growth of the quaternary AlGaInAs on an InP substrate by molecular beam epitaxy had an equal aluminum-to-gallium mole fraction ratio, and exhibited a 5 K bandgap energy of 1.237 eV. This is intermediate between the 5 K band gap energy of Ga<inf>0.47</inf>In<inf>0.53</inf>As (0.810 eV) and that of Al<inf>0.48</inf>In<inf>0.52</inf>As (1.56 eV). A Schottky diode and a MESFET were fabricated on this material.

The steady-state optical response of the homojunction triangular barrier photodiode

The n-type homojunction triangular barrier photodiode (TBP) is shown to have an extremely high optical gain of several thousands. This high gain at low light levels is shown to result from the low thermal generation rate of holes in the active region of the TBP, indicating a small concentration of deep traps in the material. A detailed analysis of the dependence of responsivity on applied voltage bias, incident optical power level, and physical device parameters has been made. This analysis indicates that the bandwidth of the TBP can be increased by either increasing the applied bias or by significantly increasing the intensity of the incident light.

Resistivity increase in MBE Ga 0.47 In 0.53 As following ion bombardment

Resistivity increase was compared following various doses of different 100 kV ions implanted into Ga0.47In0.53As. The largest resistivity increase of n-type Ge doped GaInAs resulted from a boron ion implant, and increased to a total of 280 times the original resistivity after heating for 15 minutes at 200°C. Boron ion bombardment can be used to isolate devices in a planar GaInAs integrated circuit process.

VB-7 the modulation doped GaInAs/AlInAs MESFET

Our objective was to make a modulation doped GaInAs MESFET using doped AlInAs between the aluminum gate and the GaInAs channel. Dingle et al. [ l ] first pointed out the enhanced electron mobility in GaAs/AlGaAs superlattice systems with planar electron gases. Mimura et al. [21 reported a high electron mobility transistor (HEMT) in GaAs/AlGaAs in which they observed significant improvement in their transistor characteristics at 77K as opposed to those at room temperature. Cheng et al. [31 has reported enhanced mobility in the GaInAs/AlInAs system in which the AlInAs was doped and conduction occurred in the GaInAs.

WA-B8 Double-heterostructure Ga 0.47 In 0.53 As MESFET's

G a 0 , 4 ~ I n o . ~ ~ A s layers lattice matched to InP show 50 percent higher low-field mobilities than GaAs for the same doping levels at 300 K.3 It was shown experimentally that the addition of P in GaInAs system decreases the low-field mobility ~ignificantly.~ This makes Gao.471no.53 As a very attractive alloy in the InGaAsP system for MESFET applications. In this paper, we report the successful fabrication of Ga0.4~Ino.53As MESFET’s. Since metal Schottky-barrier heights (&) on Gao.471no.53As are too low (-0.30 eV) to be used in MESFET gates, Alo.481no.52As, which has a 1.46-eV direct bandgap and a higher &,(-0.80 eV), was used as a thin intermediary layer between metal and GaInAs to increase @ b . A10.481n0.52A~, which lattice matches InP, was also used for electron-confining buffer layers, as it can be expected to have a lower electron affinity than GaInAs. Al/AlInAs/GaInAs/ AlInAs double-heterostructures grown on (100) InP semiinsulating substrates were used for FET fabrication. All layers were grown by MBE without exposure to air, including the single-crystal epitaxial A1 metal. The devices had 0.6-pm gate lengths, 6 5 ~ m effective gate widths, 0.8ym source-gate spacings, and 3.5-pm source-drain spacings. The AlInAs layer underneath the gate was 600 thick, and the high sheetresistance AlInAs buffer layer was 1000 A. The GaInAs active layer was 1450 A thick doped with germanium to 1.2 X IO1’ ~ m ~ . The average dc. transconductance (g, ) for a number of devices was 135 ms/mm at VGS = 0 V and V ~ S = 2 V, which is significantly higher than g, = 100 ms/mm for GaAs MESFET’s with the same doping level. At VGS = 0 V and VDs = 4 V, average g , was 230 ms/mm where weak avalanching was noticeable. The average pinchoff voltage was -2.2 V, while the average knee voltage was 0.95 V. No backgating effect has been observed. Further improvement in g , should be obtained by thinning the Schottky-assist AlInAs layer to minimize the gate-voltage drop across it, since the layer used in these experiments was thicker than necessary. This device should operate at higher frequencies than the maximum frequency of GaAs MESFET’s because of the higher g, , together with the smaller source-to-gate capacitance resulting from the high-resistance AlInAs layer between metal and GaInAs.