Investigation of indium doping and incorporation in AlGaAs/GaAs double-barrier resonant tunnelling structures

In doping and incorporation in the barrier layers of AlGaAs/GaAs double-barrier resonant tunnelling structures (DBRTSs) have been studied. It was found that the peak-to-valley current ratio (PVCR) can be improved by the proper amount of In doping. This is attributed to the improvement in the quality of the AlGaAs barrier layers due to the high surface migration rate of In atoms that reduces group III vacancies. Also pseudomorphic In/sub x/(Al/sub 0.5/Ga/sub 0.5/)/sub 1-x/As/GaAs (x=0.12) strained-layer DBRTSs have been fabricated by incorporating a sufficient amount of In into the AlGaAs barrier layers. PVCRs as high as 27.5 at 77 K have been obtained. This is the first realisation of such DBRTSs with lattice-mismatched quaternary barrier layers.<>     

Thermal stability of Al/AlGaAs and Al/GaAs/AlGaAs (MBE) Schottky barriers

Outstanding stability has been observed in Al/Al/sub x/Ga/sub 1-x/As and Al/GaAs/Al/sub x/Ga/sub 1-x/As (x=0.25) Schottky barriers prepared by depositing Al in situ by MBE on annealing up to 400 degrees C. Conventionally evaporated barriers have been fabricated and compared with epitaxial ones. The changes in barrier height and ideality factor induced by annealing are reported.<>     

Negative differential resistance of GaAs/Al/sub x/Ga/sub 1-x/As multiquantum well structures under high power photoexcitation: structure optimisation for an oscillator

A study is presented of the photocurrent behaviour of p-i-n diodes having GaAs/Al/sub x/Ga/sub 1-x/As MQW absorption regions for varying incident power, incident wavelength and barrier height, given by the Al fraction x. Optimum results for applications in high power oscillators are expected to be obtained for 0.1>     

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.     

High breakdown voltage AlAs/InGaAs quantum barrier varactor diodes

Data are presented on single quantum barrier AlAs/In/sub 0.53/Ga/sub 0.47/As varactor diodes intended as submillimetre wavelength frequency multipliers that exhibit extremely high breakdown voltage and excellent capacitance modulation characteristics. Record breakdown voltages as high as 12 V were achieved with a composite 50AA/50AA/50AA thick In/sub 0.52/Al/sub 0.48//AlAs/In/sub 0.52/Al/sub 0.48/As barrier sandwiched between 3000 AA(1.2*10/sup 17/ cm/sup -3/) In/sub 0.53/Ga/sub 0.47/As depletion regions.<>     

Double heterojunction bipolar transistor in Al/sub x/Ga/sub 1-x/As/GaAs/sub 1-y/Sb/sub y/ system

Double heterojunction bipolar transistors based on the Al/sub x/Ga/sub 1-x/As/GaAs/sub 1-y/Sb/sub y/ system are examined. The base layer consists of narrow band gap GaAs/sub 1-y/Sb/sub y/ and the emitter and collector consist of wider band gap Al/sub x/Ga/sub 1-x/As. Preliminary experimental results show that AlGaAs/GaAsSb/GaAs DHBTs exhibit a current gain of five and a maximum collector current density of 5*10/sup 4/ A/cm/sup 2/.<>     

Low-temperature MBE-grown In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As/InP optical waveguides

The MBE growth of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As ( lambda /sub g/=1.06 mu m) layers in the temperature range of 400-450 degrees C was demonstrated to give high-quality optical waveguides which not only exhibit low propagation losses as low as 0.5 dB/cm at lambda =1.55 mu m but concomitantly high resistivity of >10/sup 4/ Omega cm. The refractive index of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As was estimated to be 3.207+or-0.03 at lambda =1.55 mu m.<>     

Fabrication of InGaP/Al/sub 0.98/Ga/sub 0.02/As/GaAs oxide-confined collector-up heterojunction bipolar transistors

A partially oxidized Al/sub 0.98/Ga/sub 0.02/As layer was introduced between the emitter and base of collector-up heterojunction bipolar transistors (C-up HBTs) to suppress the leakage current and improve the current gain. Dependence of device current gain and leakage current on oxidation temperature was investigated. At lower oxidation temperature, the current gain can be effectively improved. Current gain and base sheet resistance were 79 and 203 ohm/sq. for the C-up HBT oxidized at 400/spl deg/C.     

BCB-bridged distributed wideband SPST switch using 0.25-/spl mu/m In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As metamorphic HEMTs

In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As metamorphic high-electron mobility transistor (mHEMT) dc-30 GHz distributed single-pole-single through (SPST) switches were designed and fabricated using the low-/spl kappa/ benzocyclobutene (BCB) bridged technology. The current gain cutoff frequency, and the electron transit time of In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As mHEMTs have been investigated. By analyzing the extrinsic total delay time, the effective velocity of electrons can be estimated, and the average velocity is 2.3/spl times/10/sup 7/cm/s. The dc-30 GHz distributed wideband SPST switch exhibits an insertion loss of less than 5.5 dB, and an isolation larger than 30 dB, which is the first demonstration of the high-isolation of InAlAs-InGaAs mHEMTs monolithic switch. As to the power performance, this switch can handle the power up to 12 dBm at 2.4 GHz. After over 250 h of 85-85 (temperature =85/spl deg/C, humidity =85%) environmental evaluation, this BCB passivated and bridged microwave and monolithic integrated circuit switch demonstrates reliable RF characteristics without any significant performance change, which proves that this process using the low-/spl kappa/ BCB layer is attractive for millimeter-wave circuit applications.     

Performance improvement in tensile-strained In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As metamorphic HEMT

This paper proposes a In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As (x=0.3-0.5-0.3) metamorphic high-electron mobility transistor with tensile-strained channel. The tensile-strained channel structure exhibits significant improvements in dc and RF characteristics, including extrinsic transconductance, current driving capability, thermal stability, unity-gain cutoff frequency, maximum oscillation frequency, output power, power gain, and power added efficiency.     

InP衬底AlAs/In0.53Ga0.47As RTD的研制

报道了InP衬底AlAs/In0.53Ga0.47As/AlAs两垒一阱结构共振隧穿二极管(RTD)器件的研制.结构材料由分子束外延制备,衬底片为(001)半绝缘InP单晶片,器件制作选用台面结构.测得室温下的峰值电流密度为1.06×105 A/cm2,峰-谷电流比为7.4,是国内报道的首例InP材料体系RTD器件.     

High-temperature (T=490 K) operation of 5.8 /spl mu/m quantum cascade lasers with InP/GaInAs waveguides

5.8 /spl mu/m Ga/sub 0.4/In/sub 0.6/As/Al/sub 0.56/In/sub 0.44/As strain-compensated quantum-cascade lasers with InP and GaInAs cladding layers using solid-source molecular-beam epitaxy have been fabricated. Low threshold current densities and high-temperature operation of uncoated devices, with a record value of 490 K, have been achieved in pulsed mode.     

Refractive index step and optical confinement in Ga/sub 0.86/In/sub 0.14/As/sub 0.13/Sb/sub 0.87//Ga/sub 0.73/Al/sub 0.27/As/sub 0.02/Sb/sub 0.98/ double heterostructure lasers emitting at 2.2 mu m

Using theoretical fitting to measured transverse far field patterns in Ga/sub 0.86/In/sub 0.14/As/sub 0.13/Sb/sub 0.87//Ga/sub 0.73/Al/sub 0.27/As/sub 0.02/Sb/sub 0.98/ DH lasers emitting at 2.2 mu m the authors estimated the value of the active layer refractive index as 3.78. This value, higher than assumed earlier based on theoretical calculations, ensures good optical confinement for this kind of heterostructure and provides a good theoretical fit with the authors' experimental data of threshold current density against active layer thickness.<>     

Temperature dependence of breakdown and avalanche multiplication in In/sub 0.53/Ga/sub 0.47/As diodes and heterojunction bipolar transistors

The avalanche multiplication and impact ionization coefficients in In/sub 0.53/Ga/sub 0.47/As p-i-n and n-i-p diodes over a range of temperature from 20-400 K were measured and shown to have negative temperature dependence. This is contrary to the positive temperature dependence of the breakdown voltage measured on InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistors (HBTs) in this and previous works. It is shown that the collector-base dark current and current gain can be the overriding influence on the temperature dependence of breakdown in InP/In/sub 0.53/Ga/sub 0.47/As HBTs and could explain previous anomalous interpretations from the latter.     

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).     

Monolithic AlAs-InGaAs-InGaP-GaAs HRT-FETS with PVCR of 960 at 300 K

This letter reports the significant N-shaped negative-differential resistance characteristics with three-terminal controllability of a monolithic heterostructure resonant tunneling field-effect transistor, realized by integrating the AlAs-In/sub 0.25/Ga/sub 0.75/As-AlAs double-barrier single-well resonant tunneling (RT) structure into the drain regime of the In/sub 0.49/Ga/sub 0.51/P-In/sub 0.25/Ga/sub 0.75/As-GaAs /spl delta/-high-electron mobility transistor. A peak-to-valley current ratio in excess of 960 at room temperature has been demonstrated, with a peak current density (J/sub p/) of 50.6 mA/mm, and a valley current density (J/sub v/) of 52.7 /spl mu/A/mm, respectively, with a transistor gate length of 1.0 /spl mu/m. The maximum current drive density was observed to be 478 A/mm-cm/sup 2/.     

alpha factor improvements in high-speed p doped In/sub 0.35/Ga /sub 0.65/As/GaAs MQW lasers

The authors investigate experimentally for the first time the improvements in the linewidth enhancement factor, alpha , resulting from simultaneous addition of strain and p-doping in high-speed GaAs-based multiquantum well lasers. The alpha factor is determined from measured changes in both gain and refractive index as a function of CW bias current, yielding alpha 3.1 and 1.4 at the threshold lasing wavelength for unstrained GaAs/Al/sub 0.25/Ga/sub 0.75/As and p-doped strained In/sub 0.35/Ga/sub 0.65/As/GaAs devices, respectively.<>     

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.     

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.     

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.<>