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We demonstrated the electro-optical characteristics of gallium nitride (GaN)-based ultraviolet (UV) light emitting diodes (LEDs) with sputtered aluminum nitride (AlN) nucleation layer. The introduction of the ex situ sputtered AlN nucleation layer improved the crystal quality of the GaN and the n-AlGaN layer of the GaN-based UV LEDs. Hence, the 20-mA output power of UV LEDs with ex situ AlN nucleation layers is higher than that of UV LEDs with GaN nucleation layers. In addition, the enhanced power output of UV LEDs with ex situ AlN nucleation could reach around 52% in magnitude at peak emission wavelengths of 370 nm compared with power outputs of UV LEDs with GaN nucleation layers. Furthermore, UV LEDs with ex situ AlN nucleation show improved reliability. The UV LEDs with ex situ AlN nucleation layer revealed a power output drop of around 9% within 168 hours , which is less than the around 14% power drop of UV LEDs with GaN nucleation layer.

An AlGaInP multi-quantum-well (MQW) light-emitting diode (LED) with a direct Ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. By the deposition of an AuBe metallic thin layer on the surface of Mg-doped GaP window layer, followed by a thermal activation process, a direct Ohmic contact between ITO and p-GaP layers can be obtained. Experimentally, under an injection current of 20 mA, a dynamic resistance of 5.7 ? and a forward voltage of 1.91 V, are obtained. In addition, a higher external quantum efficiency of 9.7% and a larger maximum light output power of 26.6 mW are found for the studied LED. As compared with the conventional LED without this structure, the external quantum efficiency of the studied device is increased by 26% under the injection current of 100 mA. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior is not degraded by using this AuBe diffused layer for the studied LED under a 20 mA operation condition.

An interesting two-step passivation (with ledge structure and sulphide based chemical treatment) on base surface, for the first time, is demonstrated to study the temperature-dependent DC characteristics and noise performance of an InGaP/GaAs heterojunction bipolar transistor (HBT). Improved transistor behaviors on maximum current gain βmax, offset voltage ΔVCE, and emitter size effect are obtained by using the two-step passivation. Moreover, the device with the two-step passivation exhibits relatively temperature-independent and improved thermal stable performances as the temperature is increased. Therefore, the two-step passivationed device can be used for high-temperature and low-power electronics applications.

The temperature-dependent characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor (HFET), using the (NH/sub 4/)/sub 2/S/sub x/ solution to form the InGaP surface passivation, are studied and demonstrated. The sulfur-passivated device shows significantly improved dc and RF performances over a wide temperature range (300-510 K). With a 1/spl times/100-/spl mu/m/sup 2/ gate-dimension HFET by (NH/sub 4/)/sub 2/S/sub x/ treatment, the considerably improved thermal stability over dc performances including lower temperature variation coefficients on the turn-on voltage (-1.23 mV/K), the gate-drain breakdown voltage (-0.05 mV/K), the gate leakage current (1.04 /spl mu/A/mm/spl middot/K), the threshold voltage (-1.139 mV/K), and the drain-saturation-current operating regimes (-3.11/spl times/10/sup -4//K) are obtained as the temperature is increased from 300 to 510 K. In addition, for RF characteristics, the sulfur-passivated device also shows a low degradation rate on drain-saturation-current operating regimes (-3.29/spl times/10/sup -4//K) as the temperature is increased from 300 to 400 K. These advantages provide the promise for high-speed high-frequency high-temperature electronics applications.

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.

The temperature-dependent DC characteristics of InGaP-GaAs heterojunction bipolar transistors with and without sulfur treatment are systematically studied and demonstrated. Due to the use of sulfur passivation, the series resistance of base-emitter junction of studied device can be effectively reduced. In addition, the device with sulfur treatment can be operated under ultra low collector current regimes (I/sub C//spl les/10/sup -11/ A). Experimentally, a long-time sulfur treatment is not appropriate. In this work, the studied device with sulfur treatment for 15 min is a good choice. Furthermore, at measured temperature (298 K-398 K), the studied device with sulfur treatment can reduce collector-emitter offset voltage and the impact of emitter size effect. Moreover, as the temperature is increased, the device with sulfur treatment will exhibit higher DC current gain and more stable temperature-dependent performances. This will extend the application regimes of the studied device in low-power and communication systems.

InGaP/InGaAs double doped channel heterostructure field-effect transistors (DDCHFETs) with δ-doped channels and uniformly doped channels are comprehensively studied and demonstrated. From the simulation results, based on a two-dimensional simulator of Atlas, the band diagrams, DC and RF characteristics of studied devices are compared and studied. The better drain current drivability, higher transconductance and microwave performances are obtained in the studied device with δ-doped channel. In addition, experimentally, the DDCHFET with δ-doped quantum well channel is fabricated successfully. Due to the employed InGaAs double δ-doped channel structure and Schottky behaviours of InGaP 'insulator', good DC properties including pinch-off and saturation characteristics, higher and linear transconductance, and good RF properties are obtained. Moreover, the experimental results are consistent with simulated data.

The dc performances of a novel InP-InGaAs tunneling emitter bipolar transistor (TEBT) are studied and demonstrated. The studied device can be operated under an extremely wide collector current regime larger than 11 decades in magnitude (10/sup -12/ to 10/sup -1/ A). A current gain of 3 is obtained even operated at an ultralow collector current of 3.9/spl times/10/sup -12/ A (1.56 /spl times/10/sup -7/ A/cm/sup 2/). The common-emitter and common-base breakdown voltages of the studied device are higher than 2 and 5 V, respectively. Furthermore, a very low collector-emitter offset voltage of 40 mV is found. The temperature-dependent dc characteristics of the TEBT are measured and studied. Consequentially, based on experimental results, the studied device provides the promise for low-power electronics applications.

The temperature-dependent characteristics of an n+-InGaAs/n-GaAs composite doped channel (CDC) heterostructure field-effect transistor (HFET) have been studied. Due to the reduction of leakage current and good carrier confinement in the n+-InGaAs/n-GaAs CDC structure, the degradation of device performances with increasing the temperature is insignificant. Experimentally, for a 1 x 100 μm2 device, the gate-drain breakdown voltage of 24.5 (22.0) V, turn-on voltage of 2.05 (1.70) V, off-state drain-source breakdown voltage of 24.4 (18.7) V, transconductance of 161 (138) mS/mm, output conductance of 0.60 (0.60) mS/mm, and voltage gain of 268 (230) are obtained at 300 (450) K, respectively. The shift of Vth from 300 to 450 K is only 13 mV. In addition, the studied device also shows good microwave performances with flat and wide operation regime.

A new S-shaped switch based on the InP/InGaAlAs material system has been successfully fabricated and demonstrated. Due to the avalanche multiplication and potential redistribution process, the interesting multiple-negative-differential-resistance (MNDR) is found under the inverted operation mode at room temperature. The three-terminal NDR characteristics are investigated under the applied base current I B . Moreover, the anomalous multiple-route and multiple-step current-voltage (I-V) characteristics at 77K are also observed. The switching behaviors demonstrate that the proposed structure is a good candidate for multiple-valued logic applications.

We propose two InGaP/GaAs resonant tunneling bipolar transistors (RTBT's) with different superlattice (SL) structures in the emitters. Based on the calculations of transmission probability, the ground-state and first excited-state minibands are estimated. The electron transmission through SL structures is significantly determined by the electric field behaviors across the barriers. The specific designs of barrier width in the SL structures are responsible for two electron transport mechanisms of sequential RT conduction associated with the minibands. Experimentally, at higher current levels, the double- and quaternary-negative difference resistance (NDR) phenomena are respectively observed for both devices at 300K. Furthermore, the experimental results are in good agreement with the theoretical prediction.

A new heterostructure field-effect transistor (HFET) with GaAs/InGaP camel-like gate and GaAs/InGaAs channel structure has been fabricated by MOCVD. The studied device exhibits a large barrier height, high breakdown voltage, and low leakage current even at high temperature environments. Experimentally, for a 1×100 μ m 2 device, the gate-drain breakdown voltage and gate leakage current are 52 (31.5) V, and 37 μ A/mm (3.5 mA/mm) at the gate-drain voltage of 40 V, respectively, at the temperature of 300 (480) K. The high drain-source operation voltage over 20 V with low leakage current is also obtained. These good performances provide the promise for high-breakdown and high-temperature operations.

A novel narrow-base heterojunction bipolar transistor and a multiple-state switching device based on the InP/InGaAlAs material system have been fabricated and demonstrated. Common-emitter current gains up to 28 and 25 are obtained. Due to the use of an InGaAlAs narrow base, interesting topee-shaped current-voltage characteristics presented in the transistor active regime and negative-differential-resistance (NDR) loci are observed under the applied base current of IB = 2 µA/step. In addition, multiple-route and multiple-state S-shaped NDR characteristics are observed at 77 K due to the insertion of the InGaAs quantum well in the base-collector junction. The topee-shaped NDR phenomena are attributed to the modulation of the potential spike at the base-emitter heterojunction. However, the switching behaviours are due to the avalanche multiplication, confinement effect and two-stage barrier lowering effect.

A new field-effect transistor using a high-barrier n/sup +/ -GaAs/p/sup +/-InGaP/n-GaAs camel-like gate and GaAs/InGaAs heterostructure-channel has been fabricated successfully and demonstrated. Experimentally, an ultra high gate-drain breakdown voltage of 52 V, a high drain-source operation voltage over 20 V with low leakage currents, and a high drain-source off-state breakdown voltage of 39.7 V are obtained for a 1/spl times/100 /spl mu/m/sup 2/ device. The high breakdown behavior is attributed to the use of high barrier camel-like gate and heterostructure channels to reduce the undesired leakage current. Furthermore, the studied device also shows high breakdown behavior in a high temperature environment and good microwave characteristics. Therefore, based on these characteristics, the studied device is suitable for high-breakdown, low-leakage, and high-temperature applications.

A newly designed high-barrier-gate Ga0.51In0.49P/InxGa1-xAs/GaAs pseudomorphic transistor with a step-compositioned channel (SC2) and bottomside delta-doped sheet (BD2S) structure has been fabricated successfully and studied. For a 1×100 µm2 studied device, a high gate-to-drain breakdown voltage over 30 V is found. In addition, an available output current density up to 826 mA mm-1 at a high gate voltage of 2.5 V, a maximum transconductance of 201 mS mm-1 with a very broad transconductance operation regime of 3 V of gate bias (565 mA mm-1 of drain current density) and a high dc gain ratio of 575 are obtained, simultaneously. Meanwhile, the maximum values of the unity current-gain cut-off frequency fT and oscillation frequency fmax are 16 and 34 GHz, respectively.

An interesting GaN-based light emitting diode (LED) using a 50 nm indium oxide (In2O3)/250 nm indium-tin oxide (ITO) mixed structure to replace the commonly used ITO (250 nm) current spreading layer is fabricated and studied. Use of the In2O3 layer could reduce the contact resistance of p-GaN in LEDs. In addition, this highly-resistive In2O3 layer, below the ITO layer could improve the current spreading performance. Experimentally, at room temperature, using this mixed structure, the luminous and EL intensities are enhanced by 17.7 and 17.1%, respectively.

An interesting GaN-based light-emitting diode (LED) with a ten-period i-InGaN/p-GaN (5-nm/5-nm) superlattice (SL) structure, inserted between a multiple-quantum-well structure and a p-GaN layer, is fabricated and studied. This inserted SL can be regarded as a confinement layer of holes to enhance the hole injection efficiency. As compared with a conventional LED device without the SL structure, the studied LED exhibits better current-spreading performance and an improved quality. The turn-on voltage, at 20 mA, is decreased from 3.32 to 3.14 V due to the reduced contact resistance as well as the more uniformity of carrier injection. A substantially reduced leakage current (10-7-10-9 A) and higher endurance of the reverse current pulse are found. As compared with the conventional LED without the SL structure, the significant enhancement of 25.4% in output power and the increment of 5% in external quantum efficiency are observed.

An AlGaInP-based multiquantum-well (MQW) light-emitting diode (LED) with an n-type modulation-doped (MD) structure, grown by metal-organic vapor-phase epitaxy, is fabricated and studied. Experimental results indicate that a lower turn-on voltage and dynamic resistance, higher output power, and smaller wavelength shift, as compared to a conventional undoped-MQW LED, are obtained. The studied n-type MD-MQW LED also exhibits a higher external quantum efficiency of 7.2% and a larger maximum light output power. The junction temperature of the studied MD-MQW LED also shows a 12 degC reduction, at 200 mA, as compared to a conventional one. These positive results are mainly attributed to the presence of a higher electron concentration in the MD-MQW active region.

An interesting AlGaInP multiple-quantum-well light-emitting diode (LED) with a direct ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. The direct ohmic contact structure is performed by the deposition of an AuBe diffused thin layer and the following activation process on the surface of a Mg-doped GaP window layer. Experimental results demonstrate that a dynamic resistance of 5.7 Omega and a forward voltage of 1.91 V, under an injection current of 20 mA, are obtained. In addition, the studied LED exhibits a higher external quantum efficiency of 9.7% and a larger maximum light-output power of 26.6 mW. The external quantum efficiency is increased by 26% under the injection current of 100 mA, as compared with the conventional LED without this structure. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior of the studied LED, under a 20-mA operation condition, is comparable to the conventional LED without this structure.

AlGaInP multiquantum-well (MQW) light-emitting diodes (LEDs), with the n-type modulation-doped (MD) structure, were grown by metal-organic vapor-phase epitaxy. On investigation, these n-type MD-MQW LEDs exhibited a higher luminescence (2.53 lm) and a higher luminous efficiency (16.05 lm/W) than those of conventional LEDs (2.04 lm and 14.49 lm/W, respectively). The junction temperature of the MD-MQW LEDs also showed the benefits of this structure over conventional LEDs with a 14 °C reduction achieved at 150 mA.

Let $r \geqslant 0$ and $k \geqslant 1$ be integers. We say that a graph $G$ has an $r$-equitable $k$-coloring if there exists a proper $k$-coloring of $G$ such that the sizes of any two color classes differ by at most $r$. The least $k$ such that a graph $G$ has an $r$-equitable $k$-coloring is denoted by $\chi_{r=} (G)$, and the least $n$ such that a graph $G$ has an $r$-equitable $k$-coloring for all $k \geqslant n$ is denoted by $\chi^*_{r=} (G)$. In this paper, we propose a necessary and sufficient condition for a complete multipartite graph $G$ to have an $r$-equitable $k$-coloring, and also give exact values of $\chi_{r=} (G)$ and $\chi^*_{r=} (G)$., Comment: 8 pages, 1 figure

We present an efficient vertical InGaN light-emitting diode (LED) in which the proposed vertical LEDs were fabricated with patterned sapphire substrates (PSS) using thinning techniques. After the thinning of sapphire substrate, selective dry etching process was performed on the remainder sapphire layer to expose the n-GaN contact layer instead of removing the sapphire substrate using the laser lift-off technique. These processes feature the LEDs with a sapphire-face-up structure and vertical conduction property. The PSS was adopted as a growth substrate to mitigate the light-guided effect, and thereby increase the light-extraction efficiency. Compared with conventional lateral GaN LEDs grown on PSS, the proposed vertical LEDs exhibit a higher light output power and less power degradation at a high driving current. This could be attributed to the fact that the vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction.

A n+-GaAs/p+-In0.49Ga0.51P/n-GaAs camel-like gate structure has been applied to fabricate high-performance transistors. The studied heterostructure field-effect transistor exhibits a large barrier height, high breakdown voltage, low leakage current, and good temperature-dependent characteristics. Experimentally, for a 1×100 μm2 device, the gate-drain breakdown voltage and gate leakage current are 52 (31.5) V, and 37 μ A/mm (3.5 mA/mm) at the gate-drain voltage of 40 V, respectively, at the temperature of 300 (480) K. In addition, the high drain-source operation voltage over 20 V with low leakage current is obtained.

A {\it linear k-forest} is a graph whose components are paths with lengths at most $k$. The minimum number of linear $k$-forests needed to decompose a graph $G$ is the {\it linear k-arboricity} of $G$ and denoted by $la_{k}(G)$. In this paper, we settle the cases left in determining the linear $2$-arboricity of the complete graph $K_n$. Mainly, we prove that $la_{2}(K_{12t+10})=la_{2}(K_{12t+11})=9t+8$ for any $t \geq 0$.

The conventional architecture suffers significant timing overhead due to system clock skew and logic path unbalance, which in turn decreases the performance of a circuit. This paper presents a design of high-speed Baugh-Wooley multiplier based on skew-tolerant domino. From simulation results, it is demonstrated that the performance is improved.

Temperature-dependent DC performances of InP/InGaAlAs heterojunction bipolar transistors (HBTs) using the InGaAlAs quaternary alloy as the base and collector layers are studied and reported. When compared with conventional InP/InGaAs HBTs, the device studied exhibits a higher common-emitter breakdown voltage and a lower output conductance even at high temperature. In addition, with decreasing temperature from 25 toward -196/spl deg/C, an irregular temperature behavior of current gain has been investigated.

A heterojunction bipolar transistor with superlattice emitter structure based on InP/InGaAs material system has been demonstrated. Two devices with different period of superlattice and emitter thickness were proposed. By introducing the superlattice into the emitter, the confinement of holes is enhanced. Experimentally, for higher periods of superlattice, the current gain is enhanced and more stable temperature-dependent characteristics are observed. The common-emitter current gains up to 170 and 54 are obtained for the studied devices with emitter thickness of 800/spl Aring/ and 150/spl Aring/, respectively.

A new heterostructure field-effect transistor (HFET) using an n/sup +/-GaAs/p/sup +/-In/sub 0.49/Ga/sub 0.51/P/n-GaAs high-barrier-gate structure has been fabricated successfully and demonstrated. The heavily doped p/sup +/-In/sub 0.49/Ga/sub 0.51/P layer is introduced to increase the barrier height and to suppress the tunneling current. Therefore, the leakage current is reduced and breakdown voltage is improved substantially. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ device, a high gate-drain breakdown voltage of 52 V and high drain-source operation voltage of 20 V with low leakage current are obtained. The high breakdown characteristics of the studied device indicate that devices with n/sup +/-GaAs/p/sup +/-In/sub 0.49/Ga/sub 0.51/P/n-GaAs high-barrier-gate structure are suitable for high-power circuit applications.

We have presented a high-performance InGaP/In/sub x/Ga/sub 1-x/As pseudomorphic high electron mobility transistor (PHEMT) in this work. Due to the presence of inverted delta-doped V-shaped InGaP/In/sub x/Ga/sub 1-x/As structure, the good carrier confinement together with high-breakdown voltage and a flat and wide transconductance operation regime are expected. Experimentally, the fabricated device (1/spl times/100 /spl mu/m/sup 2/) shows a high gate-to-drain breakdown voltage of 30 V and a high output drain saturation current density of 826 mA/mm at V/sub GS/=2.5 V. The high transconductance expands over a very broad operation range with the maximum value of 201 mS/mm. Meanwhile, the studied device exhibits a good microwave frequency linearity.