A. Mesquida Kusters

Al-free InP-based high electron mobility transistors: Design, fabrication and performance

Abstract We review the design, fabrication and performance of LP-MOVPE grown Al-free InP/In x Ga 1 − x As/InP (53% ≤ x ≤ 81%) high electron mobility transistors (HEMTs) with two types of barrier-enhancement layers; (1) a lattice-matched p + -type doped InP quasi-Schottky barrier layer (junction-modulated HEMT or JHEMT) and (2) a strained undoped In 0.75 Ga 0.25 P Schottky barrier layer (conventional HEMT). First, the advantages and drawbacks of Al-free InP-HEMTs are summarized from the physical point of view and compared with the conventional InAlAs/InGaAs/InP material system. After a short description of the fabrication process a typical layer structure is shown and the optimum parameters for each layer are deduced with the help of different characterization methods. Thereby, special attention is given to the influence of the In-mole fraction in the InGaAs channel on the DC- and RF-performance of 1 μm gate-length devices. In a later section, the limits concerning the application of JHEMTs in ultra-high speed circuits are discussed and results of devices with L G down to 0.18 μm are shown. As one solution to shortening the gate length without the appearance of negative short channel effects, devices with u-In 0.75 Ga 0.25 P as barrier-enhancement layer and L G = 0.25 μ m are presented. Finally, the RF-performance between GaAs- and InP-based HEMTs and our devices is compared. This comparison demonstrates the excellent potential of Al-free InP-HEMTs for microwave and mm-wave applications.

MOVPE growth of III–V compounds for optoelectronic and electronic applications

Abstract This paper reviews some of the most important aspects of MOVPE of III–V semiconductors. The paper starts with fundamental aspects of MOVPE in general, and turns to the use of novel precursors and precursor combinations with special emphasis on improvements in safety, material consumption, reactivities or precursor combinations and layer purity. The next section discusses special problems and advantages of selective area growth and growth on patterned substrates. Then the growth of heterostructures, quantum wells and superlattices for field-effect transistors, Wannier-Stark modulators and resonant tunnelling diodes is described. It will be shown that different growth parameters, e.g. different switching sequences between individual layers, are needed for either optoelectronic or electronic devices. The usefulness of MOVPE for various material combinations such as AlGaAs/GaAs, InP/InGaAs, InGaAs/InGaAs, InGaAsP/InGaAsP, InAs/AlSb and InAs/InPSb will be demonstrated by material properties and device performances.

In‐plane effective masses and quantum scattering times of electrons in narrow modulation‐doped InGaAs/InP quantum wells

In‐plane effective masses m*∥ and quantum scattering times are derived from temperature‐dependent Shubnikov–de Haas oscillations measured on a series of modulation‐doped InxGa1−xAs/InP quantum wells with x=0.53 and 0.75, and for well widths ranging from 3 to 7 nm. The values for m*∥ are consistently higher by 30%–70% than the respective bulk data. This result is in good agreement with recent theoretical calculations which predict an increase of m*∥ with decreasing well width. The scatter of the mass values for nominally identical quantum wells is assumed to reflect corresponding variations of the well widths. The ratio of quantum to classical scattering times and the carrier density dependence of the electron mobilities indicate that Coulomb scattering is important even in extremely narrow quantum wells.

Charge collection efficiencies and reverse current densities of GaAs detectors

Abstract GaAs surface barrier diodes with different areas have been fabricated and tested as particle detectors. It is shown that the reverse current is affected both by the area of the Schottky contact and by its circumference. The charge collection properties can be explained on the basis of a model that takes into account trapping effects and the distribution of the electric field within the detector. From this model (several) rules for optimizing GaAs detectors are derived.

Characterization of hetero interfaces in InP/In/sub 75/Ga/sub 25/As/InP HFETs by means of digital signal processing of measured low frequency noise spectra

Modern HFETs exhibit very low microwave noise due to the spatial separation of the donor layer and the channel. However, these devices suffer from their low frequency (LF) noise, which limits their applicability both as mixers and as wideband amplifiers. We are interested in the characterization and localization of LF-noise sources in InP/InGaAs/InP HFETs. Because the noise contribution of the aluminium DX-centers is eliminated, we believe that the measured 1/f-noise mainly results from the InP/InGaAs hetero interfaces, especially from the lower one, caused by the less stable InP surface. Furthermore, deep traps may be located at the interfaces due to the gradual transition of the alloy composition. To detect these deep traps, the evaluation of LF-noise spectra seems to be a very promising method. Compared to DLTS; it offers several advantages, since the measurements may be performed near the thermodynamic equilibrium and the effect of gate-source voltage V, variations can be studied. Besides, DLTS is an indirect method and some deep levels detected with it may not contribute to the noise.<<ETX>>

Low‐ and high‐field transport properties of pseudomorphic InxGa1−xAs/InP (0.73≤x≤0.82) p‐type modulation‐doped single‐quantum‐well structures

The transport properties of three p‐type modulation‐doped InxGa1−xAs/InP (0.73≤x≤0.82) single‐quantum‐well structures grown by metalorganic chemical‐vapor deposition are reported. High carrier mobilities of μH=7800 cm2/V s coupled with total carrier concentrations of pS=2.1×1012 cm−2 were reached, for example, for x=0.73 at 5 K. Shubnikov–de Haas and quantum Hall‐effect measurements at 50 mK showed the population of two spin‐split V3/2 subbands. Using p‐modulation‐doped field‐effect transistors with a gate length of LG=1 μm, fabricated on the same samples, the carrier transport at moderate and high fields was investigated at 77 K. Thereby, the population of the heavy‐hole subband and, above a critical field, also the occupation of the light‐hole subband were verified. With the help of dc transconductance (gmext‐VGS) and magnetotransconductance measurements a decoupling between both subbands at cryogenic conditions and moderate fields was observed, resulting in two clearly defined conducting channels. Furt...

Low-frequency noise phenomena in InP-based HFETs related to stress induced degeneration and interface properties

The normalized noise power density is shown for HFETs with InAlAs as barrier layer and those where InP is used. All transistors were manufactured in our Institute using the same geometrical parameters and exhibit almost the same sheet carrier concentration in the channel. The depicted spectrum of the HFET containing InAlAs is a typical result for these devices grown by MBE as long as no degeneration effects occur. On the other hand, HFETs without aluminium which were grown by LP-MOVPE and in which the In mole fraction has been varied from 53% up to 81%, show excellent device properties. The comparison between both material systems reveals that noise of the HFET with InAlAs is slightly lower. This can be understood since during the growth of the interface in this device only one component must be exchanged. Also, due to the larger conduction band discontinuity the penetration depth of the 2DEG into the barrier is reduced and with it the activation of traps located there. The latter also explains the decreasing noise power with increasing indium portion in the channel of the aluminium-free HFETs. However, at 67% indium, the minimum is reached and further increasing the strain does not improve the noise properties. Concluding, it may be stated that there exists a trade-off dependent on the special application between the slightly better performance of the InAlAs/InGaAs/InP HFETs and those devices with a InP barrier, which are less sensitive to stress.

Hydrogen purging during growth interruptions and its effect on electron transport in InP/InGaAs/InP HFETS grown by LP-MOVPE

InP/InGaAs is a powerful material system for a variety of devices including HFETs. The quality of the heterointerface is very sensitive to growth parameters, especially to the switching sequence of the reactive gases. Improvement of the interface with respect to electron transport was achieved by growth interruptions without group-V stabilization of the surface before growth of the subsequent layer is started.<<ETX>>

Effect of indium mole fraction on charge control, DC and RF performance of single quantum-well InP/In/sub x/Ga/sub 1-x/As/InP (0.53/spl les/x/spl les/0.81) HEMTs

During the past several years, HEMT structures on InP have attracted much attention in high-speed digital and millimeter wave device applications. Devices which use In/sub x/Ga/sub 1-x/As channel on InP substrates (x/spl ges/0.53) show better performance than those on GaAs (0/spl les/x0.3) because of the enhanced low-field mobility, peak- and saturation velocities as well as carrier concentration in the case of indium-rich channels. Therefore, the most effective way to improve both DC- and RF-characteristics of these devices is to increase x as high as possible without device degradation by channel relaxation. A very promising alternative to conventional InAlAs/InGaAs/InP HEMTs are the InP/In/sub x/Ga/sub 1-x/As/InP pseudomorphic HFETs. In these devices the instable Al-containing material InAlAs is replaced by InP for both barrier and carrier supplying layers. In order to improve the Schottky characteristics on InP a thin, highly doped and depleted p-InP barrier enhancement layer is utilized. In the recent past very good results have been achieved using this approach. In this study we present a systematical investigation about the influence of excess indium in the channel of five LP-MOVPE grown single quantum-well (SQW) InP/In/sub x/Ga/sub 1-x/As/InP (x=0.53, 0.6, 0.67, 0.74 and 0.81) HEMTs.<<ETX>>

Enhanced barrier height GaInAs MSM Schottky barrier photodiodes

The p+-cap layer of InP together with 80 nm of undoped (Nb equals 5 1014 cm-3) assist layer of InP for the first time were used to increase the Schottky barrier height (up to 0.73 e.V.) on GaInAs and to create high speed MSM photodetectors on it. The average dark current density is 1.6 10-4 A/cm2 -- the lowest known value on the GaInAs semiconductor material. A rise time of 37 ps for the impulse response at (lambda) equals 1.3 micrometers was measured for a MSM diode with 2 micrometers fingers and 2 micrometers gaps and an active area of 30 X 30 micrometers 2.