Characteristics of In/sub x/Al/sub 1-x/N-GaN high-electron mobility field-effect transistor

GaN-based field effect transistors commonly include an Al/sub x/Ga/sub 1-x/N barrier layer for confinement of a two-dimensional electron gas (2DEG) in the barrier/GaN interface. Some of the limitations of the Al/sub x/Ga/sub 1-x/N-GaN heterostructure can be, in principle, avoided by the use of In/sub x/Al/sub 1-x/N as an alternative barrier, which adds flexibility to the engineering of the polarization-induced charges by using tensile or compressive strain through varying the value of x. Here, the implementation and electrical characterization of an In/sub x/Al/sub 1-x/-GaN high electron mobility transistor with Indium content ranging from x=0.04 to x=0.15 is described. The measured 2DEG carrier concentration in the In/sub 0.04/Al/sub 0.96/N-GaN heterostructure reach 4/spl times/10/sup 13/ cm/sup -2/ at room temperature, and Hall mobility is 480 and 750 cm/sup 2//V /spl middot/ s at 300 and 10 K, respectively. The increase of Indium content in the barrier results in a shift of the transistor threshold voltage and of the peak transconductance toward positive gate values, as well as a decrease in the drain current. This is consistent with the reduction in polarization difference between GaN and In/sub x/Al/sub 1-x/N. Devices with a gate length of 0.7 /spl mu/m exhibit f/sub t/ and f/sub max/ values of 13 and 11 GHz, respectively.     

Laser gain and current density in a disordered AlGaAs/GaAs quantum well

The laser gain and current density at room temperature are analysed for disordered (interdiffusion induced) Al/sub 0.3/Ga/sub 0.7/As/GaAs single quantum well structures at a carrier injection level of 4*10/sup 12/ cm/sup -2/. The results show that both the peak gain and current density remain about the same strength during the initial stages of disordering, and provide a bandwidth of 55 nm.<>     

InAs/GaAs quantum dot infrared photodetector (QDIP) with double Al/sub 0.3/Ga/sub 0.7/As blocking barriers

The ten stacked self-assembled InAs/GaAs quantum dot infrared photodetectors (QDIP) with different Al/sub 0.3/Ga/sub 0.7/As barrier widths and growth temperatures were prepared. Asymmetric current-voltage (I-V) characteristics and 2/spl sim/7.5 /spl mu/m detection window were observed. Peak responsivity of 84 mA/W at -0.4 V and peak specific detectivity of 2.5/spl times/10/sup 9/ cm-Hz/sup 1/2//W at zero bias were observed at 50 K. The characteristics of polarization insensitivity over the incident light and the high background photocurrent suggest that the self-assembled QDIP can be operated at higher temperature (/spl sim/250 K) under normal incidence condition in contrast to quantum well infrared photodetector (QWIP).     

Highly reliable GaN-based light-emitting diodes formed by p-In/sub 0.1/Ga/sub 0.9/N-ITO structure

Indium-tin-oxide (ITO) is deposited as a transparent current spreading layer of GaN-based light-emitting diodes (LEDs). To reduce the interfacial Schottky barrier height, a thin p-In/sub 0.1/Ga/sub 0.9/N layer is grown as an intermediate between ITO and p-GaN. The contact resistivity around 2.6/spl times/10/sup -2/ /spl Omega//spl middot/cm/sup 2/ results in a moderately high forward voltage LED of 3.43 V operated at 20 mA. However, the external quantum efficiency and power efficiency are enhanced by 46% and 36%, respectively, in comparison with the conventional Ni-Au contact LEDs. In the life test, the power degradation of the p-In/sub 0.1/Ga/sub 0.9/N-ITO contact samples also exhibits a lower value than that of the conventional ones.     

High breakdown voltage (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs quasi-enhancement-mode pHEMT with field-plate technology

A high breakdown voltage and a high turn-on voltage (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs quasi-enhancement-mode (E-mode) pseudomorphic HEMT (pHEMTs) with field-plate (FP) process is reported for the first time. Between gate and drain terminal, the transistor has a FP metal of 1 /spl mu/m, which is connected to a source terminal. The fabricated 0.5/spl times/150 /spl mu/m/sup 2/ device can be operated with gate voltage up to 1.6 V owing to its high Schottky turn-on voltage (V/sub ON/=0.85 V), which corresponds to a high drain-to-source current (I/sub ds/) of 420 mA/mm when drain-to-source voltage (V/sub ds/) is 3.5 V. By adopting the FP technology and large barrier height (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P layer design, the device achieved a high breakdown voltage of -47 V. The measured maximum transconductance, current gain cutoff frequency and maximum oscillation frequency are 370 mS/mm, 22 GHz , and 85 GHz, respectively. Under 5.2-GHz operation, a 15.2 dBm (220 mW/mm) and a 17.8 dBm (405 mW/mm) saturated output power can be achieved when drain voltage are 3.5 and 20 V. These characteristics demonstrate that the field-plated (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P E-mode pHEMTs have great potential for microwave power device applications.     

Calculated threshold currents of nitride- and phosphide-based quantum-well lasers

We have calculated the room temperature gain-current characteristics for a 360 nm wavelength, 80 /spl Aring/ GaN-Al/sub 0.14/Ga/sub 0.86/N and a red-emitting, 80 /spl Aring/ Ga/sub 0.51/In/sub 0.49/P-(Al/sub 0.44/Ga/sub 0.56/)/sub 0.51/In/sub 0.49/P quantum well laser structures, including many body effects. Although the carrier density and spontaneous current are much higher (by a factor of 4 and 3, respectively) in the nitride structures for a given local gain, the higher confinement factor at short wavelengths means the intrinsic threshold current of these devices is predicted to be approximately twice that of red lasers with the same optical loss.     

Surface-emitting laser diode with distributed Bragg reflector and buried heterostructure

A surface-emitting laser diode (SELD) with distributed Bragg reflector (DBR) and buried heterostructure (BH) is fabricated by the metalorganic chemical vapour deposition (MOCVD), reactive ion beam etching (RIBE) and liquid phase epitaxial (LPE) regrowth techniques. An Al/sub 0.1/Ga/sub 0.9/As/Al/sub 0.7/Ga/sub 0.3/As multilayer is employed for the lower reflector. The active region is embedded with Al/sub 0.4/Ga/sub 0.6/As current blocking layers. The threshold current is 28 mA, and the spectral width is 2.5 AA. A 2*2 array is also demonstrated.<>     

Cat-CVD SiN-passivated AlGaN-GaN HFETs with thin and high Al composition barrier Layers

The effect of SiN surface passivation by catalytic chemical vapor deposition (Cat-CVD) on Al/sub 0.4/Ga/sub 0.6/N-GaN heterostructure field-effect transistors (HFETs) was investigated. The channel sheet resistance was reduced by the passivation due to an increase in electron density, and the device characteristics of the thin-barrier HFETs were significantly improved by the reduction of source and drain resistances. The AlGaN(8 nm)-AlN(1.3 nm)-GaN HFET device with a source/drain distance of 3 /spl mu/m and a gate length of 1 /spl mu/m had a maximum drain current density of 0.83 A/mm at a gate bias of +1.5 V and an extrinsic maximum transconductance of 403 mS/mm. These results indicate the substantial potential of Cat-CVD SiN-passivated AlGaN-GaN HFETs with thin and high Al composition barrier layers.     

The microwave power performance comparisons of Al/sub x/Ga/sub 1-x/As/In/sub 0.15/Ga/sub 0.85/As (x=0.3, 0.5, 0.7, 1.0) doped-channel HFETs

The properties of doped-channel field-effect transistors (DCFET) have been thoroughly investigated on Al/sub x/Ga/sub 1-x/As/InGaAs (x= 0.3, 0.5, 0.7, 1) heterostructures with various Al mole fractions. In this study, we observed that by introducing a 200-/spl Aring/-thick Al/sub 0.5/Ga/sub 0.5/As (x=0.5) Schottky layer can enhance the device power performance, as compared with the conventional x=0.3 AlGaAs composition system. However, a degradation of the device power performance was observed for further increasing the Al mole fractions owing to their high sheet resistance and surface states. Therefore, Al/sub 0.5/Ga/sub 0.5/As Schottky layer design provides a good opportunity to develop a high power device for power amplifier applications.     

Rectification at n-n GaAs:(Ga,Al)As heterojunctions

n-n Ga0.7Al0.3As: GaAs heterojunction structures have been grown by l.p.e., with 1 × 1015 cm-3 net carriers in the ternary. N/W profiling across the heterojunction shows an accumulation region on the GaAs side and a depletion region on the (Ga, Al)As side. I/V characteristics at room temperature show significant rectification.     

纤锌矿GaN/AlxGa1-xN量子阱中自由极化子能级

采用Lee-Low-Pines (LLP)变分法研究了纤锌矿GaN/Al0.3Ga0.7N量子阱中自由极化子能量和电子-声子相互作用对自由极化子能量的影响.理论计算中考虑了量子阱中定域声子模(Confined phonon modes)和半空间声子模(Half-space phonon modes)的影响以及电子有效质...     

Improvement of InGaN/GaN laser diodes by using a Si-doped In/sub 0.23/Ga/sub 0.77/N/GaN short-period superlattice tunneling contact layer

InGaN/GaN multiple-quantum-well laser diode (LD) structures, including an Si-doped n/sup +/-In/sub 0.23/Ga/sub 0.77/N/GaN short-period superlattice (SPS) tunneling contact layer, are grown on c-face sapphire substrates by metalorganic vapor-phase epitaxy. The In/sub 0.23/Ga/sub 0.77/N/GaN(n/sup +/)-GaN(p) tunneling junction, which uses a low-resistivity n/sup +/-In/sub 0.23/Ga/sub 0.77/N/GaN SPS instead of a high-resistivity p-type GaN as a top contact layer, allows the reverse-biased tunnel junction to form a "quasi-ohmic" contact. Experimental results indicate that LDs with n/sup +/-In/sub 0.23/Ga/sub 0.77/N/GaN SPS contacting layers can achieve a lower threshold current and longer lasing duration under pulsed operation. Moreover, when the input pulse width is lengthened from 300 ns to 2 /spl mu/s, the lasing duration of the LD with Pt ohmic contact is three times longer than that of the LD with Ni/Au ohmic contacts. Therefore, we conclude that nitride-based LDs with an SPS reversed-tunneling contact layer may significantly reduce the contact resistance of an anode electrode and thereby increase the thermal stability of the device reliability.     

AlGaN MSM紫外探测器

用通过MOCVD生长的未掺杂的n-Al0．3Ga0．7N制备了金属-半导体-金属 (MSM)结构紫外探测器。器件在2．5V偏压时的暗电流为1pA,在6．5V偏压时的暗电流为1nA．在1V偏压下和298nm波长处,探测器的电流响应率为0.038A／W,在300nm 波长处有陡峭的截止边,这与文献中介绍的AlxGa1-xN探测器在x=0．3时截止波长为 300nm相一致。     

(Al/sub 0.5/Ga/sub 0.5/)/sub 0.65/In/sub 0.35/P/Ga/sub 0.65/In/sub 0.35/P double-heterostructure orange light-emitting diodes

Visible light-emitting diodes (LEDs) emitting at 615 nm and employing the AlGaInP/GaInP double heterostructure (DH) grown on a lattice-matched GaAs/sub 0.7/P/sub 0.3/ substrate have been fabricated for the first. The external quantum efficiency of 0.156% for the orange LEDs can be achieved by introducing the GaP material as the current spreader and window layer for the DH LEDs.<>     

Double heterojunction NpN GaAlAs/GaAs bipolar transistor

Double heterojunction NpN Ga0.7Al0.3As/GaAsAs/Ga0.7Al0.3-As bipolar transistors have been developed and tested. Besides a wide-gap emitter a wide-gap collector was added to form the NpN double heterojunction structure, which can be operated as a bipolar transistor in bidirection. I/V measurements show that the turn-on voltage of about 0.2 V, which is the normal case in Npn wide-gap emitter GaAsAs/Ga0.7Al0.3As transistors (common emitter), is eliminated. As compared with the Npn GaAs transistor the storage time ts of the NpN GaAs transistor is reduced by a factor of about 2.     

Polarization-Engineered Ga-Face GaN-Based Heterostructures for Normally-Off Heterostructure Field-Effect Transistors

Polarization-engineered Ga-face GaN-based heterostructures with a GaN cap layer and an AlGaN/p-GaN back barrier have been designed for normally-off field-effect transistors (FETs). The simulation results show that an unintentionally doped GaN cap and p-GaN layer in the buffer primarily deplete electrons in the channel and the Al_0.2Ga_0.8N back barrier helps to pinch off the channel. Experimentally, we have demonstrated a normally-off GaN-based field-effect transistor on the designed GaN cap/Al_0.3Ga_0.7N/GaN channel/Al_0.2Ga_0.8N/p-GaN/GaN heterostructure. A positive threshold voltage of 0.2 V and maximum transconductance of 2.6 mS/mm were achieved for 80-μm-long gate devices. The device fabrication process does not require a dry etching process for gate recessing, while highly selective etching of the GaN cap against a very thin Al_0.3GaN_0.7N top barrier has to be performed to create a two-dimensional electron gas for both the ohmic and access regions. A self-aligned, selective etch of the GaN cap in the access region is introduced, using the gate metal as an etch mask. The absence of gate recess etching is promising for uniform and repeatable threshold voltage control in normally-off AlGaN/GaN heterostructure FETs for power switching applications.     

High-performance 450-GHz GaAs-based heterostructure barrier varactor tripler

In this letter, we report on the record performance of GaAs-based heterostructure barrier varactors (HBVs) in tripler circuits. Both fabrication technique of planar Al/sub 0.7/Ga/sub 0.3/As/GaAs heterostructure barrier varactors (HBVs) and measurements of a corresponding tripler circuit are presented. Planar transmission lines on a thin dielectric membrane and flip-chip technique without air bridges provide reduced parasitic losses and, hence, higher tripler efficiency. Frequency tripler measurements have shown more than 1 mW at 450 GHz.     

Coherent operation of monolithically integrated master oscillator amplifiers

Monolithically integrated master oscillator power amplifiers have been fabricated. The oscillator is a second order distributed Bragg reflector (DBR) laser. The epitaxial layer structure consists of a double quantum well active region bonded by Al/sub 0.3/Ga/sub 0.7/As confining layers and Al/sub 0.4/Ga/sub 0.6/As cladding layers. The resultant output is a single longitudinal mode in a nearly diffraction limited output to a power level of 485 mW.<>     

Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall

In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications.     

Optimized breakdown probabilities in Al/sub 0.6/Ga/sub 0.4/As-GaAs heterojunction avalanche photodiodes

Recently, it has been shown that the noise characteristics of heterojunction Al/sub 0.6/Ga/sub 0.4/As-GaAs avalanche photodiodes (APDs) can be optimized by proper selection of the width of the Al/sub 0.6/Ga/sub 0.4/As layer. Similar trends have also been shown theoretically for the bandwidth characteristics. The resulting noise reduction and potential bandwidth enhancement have been attributed to the fact that the high bandgap Al/sub 0.6/Ga/sub 0.4/As layer serves to energize the injected electrons, thereby minimizing their first dead space in the GaAs layer. We show theoretically that the same optimized structures yield optimal breakdown-probability characteristics when the APD is operated in Geiger mode. The steep breakdown-probability characteristics, as a function of the excess bias, of thick multiplication regions (e.g., in a 1000-nm GaAs homojunction) can be mimicked in much thinner optimized Al/sub 0.6/Ga/sub 0.4/As-GaAs APDs (e.g., in a 40-nm Al/sub 0.6/Ga/sub 0.4/As and 200-nm GaAs structure) with the added advantage of having a reduced breakdown voltage (e.g., from 36.5 V to 13.7 V).