K. Heime

Lp-movpe Growth and Optical Characterization of Galnp/gaas Heterostructures: Interfaces, Quantum Wells and Quantum Wires

Lattice matched Ga0.5In0.5P/GaAs single interfaces, single quantum wells (QW) and finally quantum wires on mesa-like selective GaAs were grown by LP-MOVPE. The photoluminescence (PL) of GaInP/GaAs QW shows an anomalous emission band of high intensity below the GaAs band gap. The effect of the growth temperature, AsH3 partial pressure, gas switching sequence and growth interruption times on these new PL features was investigated. The formation of GaInPAs layers at the GaInP-to-GaAs interface, due to the substitution of P to As, is responsible for the anomaly in the luminescence. The stability of the GaInP/GaAs interfaces was checked after growth by rapid thermal annealing (RTA). Intermixing at the GaInP/GaAs heterointerfaces was also considered. The introduction of a 1 nm thick GaP barrier between the GaInP and GaAs layer was enough to suppress the GaInPAs intermediate layers and large area quantum wells and wires were successfully grown.

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>>

Vapor pressures of Y, Ba, Cu precursors for the growth of YBa2Cu3O7 by MOVPE

The vapor pressures of theβ-diketonates Y(THD), Ba(THD), and Cu(THD), commonly used as precursors for MOVPE of YBa2Cu3O7, and Y(MCP) were measured at different temperatures. A time-resolved static method recording the pressure vs. time at constant temperature was used, permitting us to deduce the vapor pressure even if the materials tend to decompose. The values of the constants of the Clausius-Clapeyron equation log10p(T)/p0=A-B/T are,A=11.7, 8.7, 8.27, 16.6 andB=4359, 2654, 3602, and 6453 K for Y(THD), Y(MCP), Ba(THD), and Cu(THD), respectively withp0= 1 Pa and temperatureT in K. The thermal stability of the sources was measured and are discussed.

InAs(PSb)-based “W” quantum well laser diodes emitting near 3.3 μm

Mid-infrared laser diodes with an active region consisting of five “W” InAsSb/InAsP/InAsSb/InAsPSb quantum wells and broad InAsPSb waveguide were fabricated by metalorganic vapor phase epitaxy on InAs substrates. Laser emission was demonstrated at 3.3 μm up to 135 K from asymmetrical structures having n-type InAsPSb and p-type InPSb cladding layers. The devices operated in pulsed regime at 3.3 μm, with a lowest threshold current density of 120 A/cm2 at 90 K, and an output power efficiency of 31 mW/facet/A. The characteristic temperature was 35 K.

Reduced incorporation of unintentional impurities and intrinsic defects in ZnSe and ZnS grown by MOVPE

In this paper we investigate the incorporation as well as the origin of unintentional impurities and intrinsic defects in ZnSe and ZnS grown by MOVPE. In ZnSe grown under optimized conditions on GaAs, we observe high electron mobilities (μ300K = 370 cm2/V·s) and low background carrier concentrations (n = 7 × 1014 cm-3). The 10 K photoluminescence (PL) spectrum shows the I2 emission and free excitons. Changes in the growth parameters cause the appearance of donor-acceptor pair recombinations at 2.72 eV. The Y-line (2.55 eV) is not observed in samples grown at temperatures below 420°C but is generated by high temperature treatment. This emission is therefore correlated to extended lattice defects such as dislocations created by strain. The so-called “Cu-green emission” (2.25−2.45 eV) not present in as-grown samples can be generated by a high temperature treatment in H2, Zn or Se atmosphere in the MOVPE reactor. From these experiments we conclude that this defect is not only due to an extrinsic impurity. ZnS grown on GaAs and ZnS substrates is dominated by free exciton recombinations. PL emission related to a free exciton bound to extrinsic donors or to an acceptor is measured. In the PL spectra of similar ZnS layers on GaAs substrate additional emissions appear. Thus this emission is related to Ga and As impurities from the substrate. The emission wavelength of the SA centre is dependent on the substrate material.

Growth of semi-insulating InP: Fe in the low pressure hydride VPE system

Abstract Growth of InP:Fe has been performed in a low pressure hydride VPE system at a total pressure of 2000 Pa. As a dopant, iron chloride obtained from an elemental iron source reacting with gaseous HCl has been used. Both the source reaction and the growth have been performed in a nitrogen ambient. Fe doping levels between 10 16 and approximately 10 20 cm -3 could be adjusted by varying the HCl flow over the iron source. The growth temperature has only a slight effect on the Fe incorporation mechanism. Additionally, the Fe incorporation is found to depend on the InP growth rate. I–V measurements reveal semi-insulating behaviour for samples with iron concentrations above 10 17 cm -3 , leading to specific resistivities in the 10 8 Ω cm region.

Photoluminescence study of interdiffusion in In0.53Ga0.47As/InP surface quantum wells

We have investigated the thermal stability and interdiffusion of In0.53Ga0.47As/InP surface quantum wells. In these structures the optically active InGaAs layer is bounded on one side by vacuum and on the other side by InP. We obtain well‐defined photoluminescence emission spectra with high intensity. After rapid thermal annealing at temperatures between 500 and 900 °C (annealing time 1 min) we observe strong emission energy shifts of up to 316 meV. By using a simple model of ion intermixing we estimate large interdiffusion coefficients (e.g., 1.7×10−14 cm2 s−1 for T=900 °C) and an activation energy of 1.3 eV for the surface quantum wells.

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.

Deposition by LP-MOVPE in the Ga-In-As-P System on Differently Oriented Substrates

Abstract We have studied the MOVPE of GaInAs and its binary constituents GaAs and InP and its binary constituents GaP and InP on InP, and on GaAs (100), (011), (111)A, (111)B oriented unmasked planar substrates in order to gain an understanding of the deposition on the bottom plane and on side wall facets of trenches in selective embedded growth. Temperature (940 K) and total pressure (20 hPa) were selected with this purpose in mind. It is shown that the behaviour of the binaries provides an understanding of the factors determining the deposition of the ternaries and that insights for selective growth on partially masked substrates can be gained from these data. In contrast to InP and InAs growth, the rates for the Ga binaries GaAs and GaP and the ternaries depend on the substrate orientation. The variation of the rates of the ternaries is very similar to that of the binary Ga constituents. More importantly, also the composition (Ga content) of the ternaries appears to track with this parameter and varies rather widely, particularly for GaInAs. In the case of selective embedded deposition the differences in rates between the different surfaces tend to be enhanced compared to those on unmasked substrates due to migration effects.

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.