A. Kohl

Double-heterojunction lattice-matched and pseudomorphic InGaAs HEMT with delta -doped InP supply layers and p-InP barrier enhancement layer grown by LP-MOVPE

The design and fabrication using low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) of a HEMT on InP substrate that only uses InP and In/sub x/Ga/sub 1-x/As as layer materials are reported. Lattice-matched (x=0.53) and strained (x=0.68) channels and a double-heterojunction design were used in this investigation. The DC performance of the 0.8- mu m devices at 300 and 77 K was excellent for both cases. Improvements of 9 and 22% in g/sub mext/ with the strain were measured at the same temperatures, in accordance with theoretical predictions. The approach described may serve as a very useful alternative, especially in MOVPE growth, to InAlAs containing structures because it eliminates many of the troublesome effects such as kinks, deep levels, interface states, high output conductances, and gate leakage, which are to a large extent attributed to impurity-Al interactions. The use of lattice-mismatched InGaAs as channel layer increases the conduction band offset to InP, the DH structure improves both confinement and current, and the p-InP barrier layer results in sufficiently high quasi-Schottky barriers.<<ETX>>

Characterization of the interface abruptness of In0.53Ga0.47As/InP multi quantum wells by Raman spectroscopy, X-ray diffractometry and photoluminescence

Abstract For lattice-matched InGaAs/InP multi quantum well structures, the interface abruptness was investigated by a combination of X-ray diffractometry, Raman spectroscopy and photoluminescence. The focus was on the effects of the gas switching parameters at the InGaAs-to-InP interface, especially the PH 3 and H 2 purging times. Ternary InAsP and quaternary InGaAsP interface layers due to carry-over and exchange effects were directly identified. Their thicknesses drastically depend on the PH 3 purging time. H 2 purging affects the interface quality to some degree, but it has only minor effects on the chemical composition at the interfaces.

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.

Quasi-Schottky barrier MSM-diode on n-Ga0.47In0.53As using a depleted p+-Ga0.47In0.53As layer grown by LP-MOVPE

Abstract An extended analysis of Schottky barrier photodiode structures on n-type Ga0.47In0.53As with a thin highly doped p-type surface layer was performed. The effective Schottky barrier height was increased by means of p+-cap layer grown by LP-MOVPE up to 0.54 eV. For the first time the MSM interdigital photodiode structures on n-InGaAs with p+-cap layer were investigated experimentally. A very low dark current density of 0.3 · 10−2 A/cm2 was obtained at ±3 V bias voltage.

Sub-half-micrometer pseudomorphic InP/In/sub x/Ga/sub 1-x/As/InP HEMT's (0.74/spl les/x/spl les/0.81) with very high f/sub T/ values

In the recent past, strained Al-free InP/In/sub x/Ga/sub 1-x/As/InP high electron mobility transistors (HEMTs) with x>53% and L/sub G//spl ges/0.5 /spl mu/m have shown very good performance mainly caused by the exceptional transport properties of electrons in In-rich In/sub x/Ga/sub 1-x/As-channel layers. In this letter we report about new results for highly strained devices with L/sub G/<0.5 /spl mu/m. Thereby, current gain cut-off frequencies of f/sub T/=100 GHz (130 GHz) for x=74% and L/sub G/=0.3 /spl mu/m at 300 K (80 K) were achieved, respectively, whereas HEMTs with x=81% and L/sub G/=0.18 /spl mu/m reached f/sub T/=131 GHz (152 GHz) at the same temperatures. Moreover, the same devices showed off- and on-state drain-source breakdown voltages of V/sub DSbr/ (OFF)=10.5 and 5 V and V/sub DSbr/ (ON)=6 and 4 V, respectively. The combination of good RF and breakdown performance prove the potential of Al-free InP-based HEMTs for power applications at mm-wave frequencies.<<ETX>>

Investigation of MOVPE-grown In0.53Ga0.47 As/InP multi-quantum wells by Raman spectroscopy and X-ray diffractometry

Abstract InGaAs/InP multi-quantum well structures, grown by metal-organic vapour phase-epitaxy, were investigated by Raman spectroscopy and X-ray diffractometry to analyse the influence of precursor gas switching parameters on the interface abruptness. Owing to carry-over effects, InAsP is formed at the InGaAs-to-InP interface for low PH 3 purging times (1 s), while for purging times greater than 4 s exchange of As by P leads to the formation of an InGaAsP interface layer, which for purging beyond 10 s saturates at a thickness of 1.2 nm.

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.

Persistent photoconductivity and electron density dependent magnetotransport measurements in narrow InGaAs/InP quantum wells

We have observed a significant persistent photoconductivity effect in narrow InGaAs/InP quantum wells grown by metalorganic vapor phase epitaxy. This effect enables a detailed study of transport parameters as a function of the electron density. In this way, the interface roughness scattering can be separated from the strongly density dependent Coulomb scattering. For different preparation conditions, we find a strong correlation between the amount of interface roughness scattering and structural data of the interface. The ratio of quantum to classical scattering times remains ≪1 even in the case when Coulomb scattering is not the predominant scattering mechanism.

InP growth on ion-implanted InP substrate: a new method to achieve selective area MOVPE

A novel method for selective area MOVPE of InP on ion-implanted InP substrate has been developed. The substrate is partially masked by photoresist, which protects the underlying surface from modification by ion implantation. On these areas the InP growth is single crystalline while a more polycrystalline phase is deposited on the implanted areas. Depending on the TMIn partial pressure, the growth rate of the single crystalline material is enhanced compared to the polycrystalline phase, which leads to selective growth at a low TMIn partial pressure and to phase selective growth at high partial pressures. The carrier mobility and the specific resistance of the polycrystalline material was found to be higher than in single crystalline InP. The ratio of the mobility in polycrystalline to the mobility in single crystalline InP depends on the growth temperature. The influence of the growth parameters, total reactor pressure, TMIn partial pressure, growth temperature and time, and the influence of the geometric dimensions was investigated. This technique should allow the growth of small structures at short distances like matrices of quantum dots or quantum wires.

Characterization of MOVPE grown InGaAsP superlattices for modulators by electron diffraction, X-ray diffraction and Z-contrast imaging

Abstract MOVPE grown ternary and quaternary Ga x In 1− x As z P 1− z heterostructures on InP substrates are increasingly used for the fabrication of, e.g. optoelectronic devices like modulators. Two of the key parameters for the performance of such devices are the crystalline quality and especially the variation of the tetragonal distortion on a nanometer scale as well as abrupt interfaces. We investigated cross-sectional specimens from nominally strain compensated quaternary superlattices (SL) of Ga x In 1−x As z P 1−z Ga y In 1−y As z P 1−z on InP substrates by convergent beam electron diffraction (CBED) and atomic number (Z)-contrast imaging using subnanometer electron probes in a field-emission scanning transmission electron microscope (STEM). While CBED allows the measurement of local strain, Z-contrast imaging combines qualitative chemical information with high spatial resolution. Additionally, X-ray diffraction (XRD) was used to characterize the layer stacks. By CBED and Z-contrast imaging we found that even small deviations from design parameters of the SL like slightly degraded interfaces and asymmetries in thicknesses and strain balance of the SL layers can give rise to degradation in device performance. The MOVPE growth process was successfully optimized to obtain abrupt interfaces in the SL, as demonstrated by XRD and Z-contrast imaging. Photocurrent spectra of this type of SL give clear evidence for the Wannier-Stark effect. So-called “oblique” transitions of the order up to 2 are observed, which demonstrates the high quality of the SL and shows the applicability as active layers in optoelectronic modulators operating at 1.55 μm.