P. Velling

InAlAs/InGaAs/InP heterostructures for RTD and HBT device applications grown by LP-MOVPE using non-gaseous sources

We report on the applicability of a fully non-gaseous source (ngs) configuration for MOVPE growth of InAlAs/InGaAs/InP heterostructures. The ngs configuration is based on TBAs/TBP/TMAs as group-V precursors and DitBuSi/CBr4 as dopant sources. Conventional group-III metalorganics and nitrogen-carrier gas are used. InAlAs/InGaAs RTD layer structures combined with carbon-doped InP/InGaAs HBT layers are characterized in detail by HRXRD measurements and simulations. The InAlAs layers exhibit n-type background concentration of n = 1.5 x 10(16) cm(-3) N = 1.7 x 10(17) cm(-3) determined by Hall and CV-measurements, respectively. Abrupt InAlAs/InGaAs heterojunction interfaces are deduced from the X-ray characterization. Fabricated RTDs exhibit a high peak current density of S-p > 1 x 10(5) A/cm(2) and a highly symmetric I-V characteristics. The RTD/HBT combination devices exhibit state-of-the-art device performance like a DC-current gain of B > 100 and a transit frequency of f(T) = 39GHz.

InP-based monolithically integrated RTD/HBT MOBILE for logic circuits

A pseudo dynamic logic family is developed on InP-substrates based on the MOBILE concept. The conventional HFET as input terminal is replaced by a monolithically integrated series combination of a HBT and a RTD forming a RTBT. This combination enables a logic function defined by the RTD area only. The HBT provides a robust enhancement type operation, although for full level compatibility a buffer inverter is still necessary. A novel distributed clocking scheme is developed. The feasibility of this logic concept is experimentally verified and an OR gate is discussed in detail.

Electro-optical examination of the band structure of ordered InGaAs

Using electroabsorption measurements, we have studied the effects of atomic superlattice ordering on the electronic band structure of InGaAs for different growth parameters. We have observed ordering-induced polarization anisotropy, valence-band splitting and band gap reduction strongest for 550 °C growth and 2°[111]B tilted substrates. Back-folded conduction-band states show an ordering dependent energy shift. The position of the split-off valence-band, however, is almost unaffected. An extension to extremely low growth temperatures exhibits ordering also for 450 °C growth. Atomic force microscopy measurements reveal a temperature-dependent change of InGaAs surface from step-like to island formation.

Metalorganic Vapour Phase Epitaxy Growth of InP-based Heterojunction Bipolar Transistors with Carbon Doped InGaAs Base Using Tertiarybutylarsine and Tertiarybutylphosphine in N2 Ambient

A process for growth of heterostructure bipolar transistors (HBT) using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) in N2 ambient is realised, which is compatible with a high temperature overgrowth, thus suitable for the vertical integration of a laser structure on top of an HBT. A high growth temperature for the C–InGaAs base is favourable, to ensure no degradation during subsequent growth. Increasing the growth temperature after the base from 500°C to 680°C within the emitter layer instead of at the base-emitter interface was found to improve the ideality factors, the dc gain and the turn-on voltage.

Sequential mechanism of electron transport in the resonant tunneling diode with thick barriers

A frequency-dependent impedance analysis (0.1–50 GHz) of an InGaAs/InAlAs-based resonant tunneling diode with a 5-nm-wide well and 5-nm-thick barriers showed that the transport mechanism in such a diode is mostly sequential, rather than coherent, which is consistent with estimates. The possibility of determining the coherent and sequential mechanism fractions in the electron transport through the resonant tunneling diode by its frequency dependence on the impedance is discussed.

High f/sub T/, high current gain InP/InGaAs:C HBT grown by LP-MOVPE with non-gaseous sources

A compositionally graded base InP/InGaAs:C HBT is grown by LP-MOVPE with novel non-gaseous source configuration. The HBT devices with an emitter area of A/sub E/=20 /spl mu/m/sup 2/ were fabricated using a novel self-aligned two metalization step technology and an B-E-C contact configuration avoiding the emitter/base air-bridge. The HBTs exhibit simultaneously a current gain cut-off frequency of f/sub T/=149 GHz and very high dc current gain up to 400. These are record results regarding dc current gain at high transit frequency.

InGaP/GaAs shadow-mask for optoelectronic integration and MBE regrowth

The epitaxial shadow mask (ESM) MBE technique has proven to yield excellent device structures with highly selective contacts. The epitaxial mask used for the ESM-MBE technique consists of a (7-8 μm) AlGaAs-layer capped by approximately I μm GaAs. These layers are lithographically patterned for the desired design. Selective etchants are used to achieve the undercut in the AlGaAs-layer. After the (re)growth, these layers have to be removed completely to get access to the grown devices. We now demonstrate a new epitaxial mask design which allows the monolithic integration of ESM-MBE grown devices with devices which are still included in the shadow mask during a first epitaxy. This demands a high bi-directional selectivity of etchants, as well as an An-free mask layer to prevent degradation problems during the processing. The lattice matched InGaP/GaAs material system (grown by LP-MOVPE) meets all these requirements (even though a thick InGaP layer has to placed on top of the mask). This is shown by a monolithically integrated version of an electro-optical n-i-p-i modulator (regrown in the mask windows) and an opto-electrical receiver, which was grown as part of the mask layers, to an all-optical smart pixel device. The receiver component, a photoconductive pinFET switch, exhibited state-of-the-art performance, e.g. a leakage current of less than 10 pA (-5 V) and a high channel conductance modulation of 10 5 .

Extension of the epitaxial shadow mask MBE technique for the monolithic integration and in situ fabrication of novel device structures

Abstract We present new methods for the in situ fabrication of novel device structures based on the epitaxial shadow mask (ESM) MBE technique. For high-quality selective contacts, the deposition of the dopants must exactly be aligned to the angular position of the substrate during growth. With a specially designed real-time software, we can either use the delta-doping (rotation and growth stopped while doping at a certain angular position) or the flash-doping technique (continuous rotation and growth with dopant shutters open in a certain angular window only). As an extension for devices where more than two selective contacts are required, an enhanced version of the shadow mask, a 2D-patterned one, is presented. In order to monolithically integrate a n–i–p–i modulator with a photoconductive switch and a reference diode, we also introduce a new technique using a special kind of shadow mask. Selective etch processes allow to integrate functional epi-layers into a “smart” shadow mask and to fabricate monolithically integrated smart pixels (MISPs), which are suitable for 2D arrays.

Cryogenic temperature dependence and modelling of RF-noise parameters of carbon doped InP/InGaAs HBT

The RF-performance of InP/InGaAs HBTs strongly depends on the ambient temperature. In this work we present the RF-noise parameters (minimum noise figure F/sub min/, equivalent noise resistance R/sub n/ and optimum generator reflection coefficient /spl Gamma/_/sub opt/) in dependence on bias condition and ambient device temperature in a range from 380 K down to 15 K. The measurement set-up used is described. Modelling of RF-parameters of carbon doped InP/InGaAs HBT is presented using a consistent small-signal and RF-noise parameter equivalent circuit.

Quantitative X-ray analysis of high performance InP/(InGa)As:C HBT for rapid non-destructive material qualification

Carbon doped InP/(InGa)As Heterostructure Bipolar Transistors (HBT) are of interest for todays (OC-768) and tomorrows (OC-3072, 100 Gbit Ethernet, UMTS) communication standards. For a reliable fabrication of these complex radio frequency (opto-)electronic circuits, a quantitative InP process technology control is necessary starting at the level of device epi-layer stacks. In this paper the quantitative characterization of an InP/(InGa)As:C HBT is carried out by non-destructive X-ray analysis. Based on X-ray measurements in 004- and 002-reflection, a detailed analysis of complex device layer stacks is purposed. As a result, an automatic calculation of layer parameters, e.g. thickness and composition is possible, reducing the turnaround time for statistical process control (SPC).