M.M. Hashemi

High-breakdown-voltage AlInAs/GaInAs junction-modulated HEMT's (JHEMT's) with regrown ohmic contacts by MOCVD

A technology for increasing both the two-terminal gate-drain breakdown and subsequently the three-terminal-off-state breakdown of AlInAs/GaInAs high-electron-mobility transistors (HEMTs) to record values without substantial impact on other parameters is presented. The breakdown in these structures is dependent on the multiplication of electrons injected from the source (channel current) and the gate (gate leakage) into the channel. In addition, holes are generated by high fields at the drain and are injected back into the gate and source electrodes. These phenomena can be suppressed by increasing the gate barrier height and alleviating the fields at the drain. Both have been achieved by incorporating a p/sup +/-2DEG junction as the gate that modulates the 2DEG gas and by utilizing selective regrowth of the source and drain regions by MOCVD. The 1- mu m-gate-length devices fabricated have two-terminal gate-drain and three-terminal-off-state breakdown voltages of 31 V and 28 V, respectively.<<ETX>>

High-performance submicrometer gatelength GaInAs/InP composite channel HEMT's with regrown ohmic contacts

This letter reports DC and RF performance of 0.25 /spl mu/m gatelength GaInAs/InP composite channel HEMTs with nonalloyed, regrown ohmic contacts by MOCVD. Regrown channel contacts are used to achieve low contact resistance (0.35 /spl Omega/-mm) to (50 /spl Aring/) GaInAs/(150 /spl Aring/) InP composite channel HEMTs. High transconductance (600 mS/mm), high full channel current (650 mA/mm), and high peak cut-off frequencies (F/sub t/=70 GHz, F/sub max/=170 GHz) are observed. Contact transfer resistance of regrown channel contacts is compared to conventional alloyed contacts for varying GaInAs/InP channel composition.

GaAs planar-doped barrier vacuum microelectronic electron emitters

A novel vacuum microelectronic electron emitter has been demonstrated in GaAs by using a planar-doped-barrier (PDB) structure. Emitted electrons are collected in high vacuum by a tantalum anode placed approximately 1 mm away from the emitter surface. Surface passivation with (NH/sub 4/)/sub 2/S/sub x/ followed by in situ heating in vacuum has been used to obtain an atomically clean surface. An emission current density of 0.42 A-cm/sup -2/ and an efficiency of 0.3% have been obtained from a 60 mu m*60 mu m emission region with an anode bias of 100 V.<<ETX>>

Rapid thermal annealing characteristics of bulk AlInAs/InP and AlInAs/GaInAs/InP high electron mobility transistor structures with planar silicon doping

The effects of high temperature rapid thermal annealing processes on carrier concentration and mobility of bulk AlInAs and AlInAs/GaInAs high electron mobility transistor structures with planar Si doping are studied. At annealing temperatures of 700 °C and 800 °C, slight reduction in mobilities and carrier concentration are observed in samples annealed with a Si3N4 cap or GaAs pieces in close proximity. The reduction in mobility is thought to be due to enhanced diffusion of the donor Si atoms towards the two‐dimensional electron gas channel. Preferential vacancy enhanced diffusion of Si atoms towards the surface is projected to be responsible for the loss in carrier concentration. At these annealing temperatures, the reduction in mobility in the samples annealed with SiO2 capping is more pronounced, and is as high as 80% at the measurement temperature of 15 K. This behavior is attributed to the outdiffusion of Ga and In atoms into the oxide thereby creating vacancies and resulting in interface mixing. Red...

High-speed p/sup +/ GaInAs-n InP heterojunction JFET's (HJFET's) grown by MOCVD

The authors report the high-frequency characteristics of a new type of InP-JFET having p/sup +/ GaInAs as the gate material grown by MOCVD (metalorganic chemical vapor deposition) using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA) as the alternative source for phosphine and arsine, respectively. Using selective wet chemical etching, heterojunction JFETs (HJFETs) with gate length of 0.6 mu m led to a unity current gain cutoff frequency and power gain cutoff frequency of 14.3 and 37.5 GHz, respectively. The large valence band discontinuity ( triangle E/sub v/ approximately=0.37 eV) considerably suppresses hole injection into the channel in the HJFET as compared to homojunction InP-JFETs, making the HJFET a preferred device for high-speed logic circuits based on JFET technology.<<ETX>>

DC and AC characteristics of a nonalloyed delta-doped MESFET by atomic layer epitaxy

The growth and fabrication of a nonalloyed delta-doped FET entirely grown by atomic layer epitaxy are reported. The DC and RF performances are shown to be comparable to similar devices fabricated on materials grown by other techniques. FETs having a gate length of 1.5 mu m show transconductances as high as 144 mS/mm at a current density of 460 mA/mm. The breakdown voltage for these devices is between 20 and 25 V for a gate-to-drain spacing of 1.6 mu m. An f/sub T/ and f/sub max/ of 13 and 19 GHz were obtained respectively. These values are among the highest values reported for MESFETs with similar geometry.<<ETX>>

High performance InP JFETs grown by MOCVD using tertiarybutylphosphine

Indium phosphide channel junction field effect transistors were fabricated by metalorganic chemical vapor deposition using tertiarybulylphosphine (TBP) as the alternative source for phosphine. At growth temperatures of 600°C, InP with specular surface morphology and mobilities as high as 61000 cm2/V s at 77Khas been achieved using trimethylindium and TBP. To improve device isolation, pinch-off characteristics, and output transconductance, we employ a high resistivity (1 × 108 Ω-cm) semi-insulating InP buffer layer using ferrocene as the Fe-dopant. Devices with gate lengths of 1 urn exhibit very high extrinsic transconductance of 130 mS/mm, gate-drain breakdown voltage exceeding 20 V, maximum current density of >450 mA/mm with record high fT and fmax of 15 GHz and 35 GHz, respectively. These results indicate: that InP JFETs are promising electronic devices for microwave power amplification, and that TBP is capable of device quality materials.

Novel fully self-aligned MESFET using source and drain regrown nonalloyed contacts by ALE

A new low temperature, nonalloyed, self-aligned FET process using regrowth technology on a patterned substrate has been demonstrated. A double 8-doped MESFET with regrown n++ source and drain contact regions using atomic layer epitaxy (ALE) were fabricated and characterized. In this novel regrowth technique, a silicide gate was embedded by molybdenum and a side wall oxide to prevent any contamination or unwanted reaction during the ALE growth. Two main features associated with our process that makes it an attractive technology for more uniform device performance across a large area wafer are: a) the refractory gate/GaAs interface is not subjected to any high temperature process, and b) nonalloyed ohmic contacts are achieved without undesirable lateral diffusion of n+ regions caused by annealing of implanted source and drain. The preliminary unoptimized device results show a transconductance of 40 mS/mm for gate length of 0.65 μn.

Effects of doping variations on electron transport in GaAs n+‐n‐n+ structures

Electron transport properties in GaAs n+‐n‐n+ structures with varying doping profiles (in the direction of electron transport) are investigated using self‐consistent ensemble Monte Carlo simulations. In particular, we study the effects of ramp doping [i.e., linearly increasing (ramp‐up) or decreasing (ramp‐down) doping density within the n region] and spike doping (i.e., introducing one or more n+ spikes in the n region) on electron transport to assess differences, advantages, and potential applications of these doping profiles on device performance. Underlying physical mechanisms for electron transport in these structures are analyzed. Simulation results reveal that overall electron transport can be improved significantly by employing ramp‐up (rather than ramp‐down) doping and multispike (instead of single‐spike) doping schemes. Potential advantages of variable doping in field‐effect transistor applications include enhanced current drive capability, reduced source resistance, and improved breakdown chara...

Impurity induced disordering of OMVPE-grown ZnSe/ZnS strained layer superlattices by germanium diffusion

We report the first confirmation of disordering of ZnSe/ZnS strained layer superlattices (SLSs) by Ge diffusion. The as-grown sample showed ±first orders of well-resolved double crystal x-ray satellite peaks due to SLS periodic structure. However, the satellite peaks completely disappeared in the Ge-diffused sample, indicating that the SLS structure was disordered by the Ge diffusion. Photoluminescence measurements at 1.4K of both the as-grown and the annealed samples without Ge diffusion show identical, sharp excitonic emission around 420 nm. After Ge diffusion, the PL peaks shift to higher energy confirming the layer disordering of the SLS.