T. Wolf

Influence of space charges on the impulse response of InGaAs metal-semiconductor-metal photodetectors

The impulse response of interdigitated metal-semiconductor-metal photodetectors fabricated on an Fe-doped InGaAs absorbing layer and an Fe-doped InP barrier enhancement layer is investigated. For ultra-short pulse excitation of 150 fs at lambda =620 nm the photoresponse is found to be less than 13 ps FWHM for detectors with 1 mu m finger spacing. Above a certain level of illumination, the peak amplitude increases sublinearly and the relative contribution of the tail to the detector response is appreciably enhanced. The screening of the electric field by photo-generated space charges is responsible for this nonlinearity. For detectors with 5 mu m finger spacing illuminated with 1.3 mu m light pulses (FWHM=33 ps), space charge perturbation of the impulse response manifests itself by a decrease of the FWHM and an increase of the fall time with increasing illumination level. The practical consequences for the performance of MSM detectors in various applications are discussed. >

Fe and Ti doping of InP grown by metalorganic chemical‐vapor deposition for the fabrication of thermally stable high‐resistivity layers

The optimum conditions for the fabrication of semi‐insulating InP epitaxial layers grown by metalorganic chemical‐vapor deposition are investigated in a comparative study of the structural, electrical, and diffusive properties of Fe‐ and Ti‐doped material. Thermally stable InP:Fe layers with resistivities approaching the intrinsic limit can be prepared in an environment of n‐type material if the Fe concentration does not exceed but is close to its solubility limit of 8×1016 cm−3 at 640 °C. In contact with p‐type layers, however, semi‐insulating characteristics of InP:Fe turn out to be difficult to reproduce because of a pronounced interdiffusion of Fe and p‐type dopants. Here, Ti doping of InP is shown to be a useful scheme for the fabrication of high‐resistivity layers. New processes for the deposition of InP:Ti using (C5H5)2Ti(CO)2 and Ti[N(CH3)2]4 as metalorganic precursors are described in detail. Ti is found to compensate up to 2×1016 cm−3 of shallow acceptors in metalorganic chemical‐vapor‐phase‐dep...

Identification of deep levels in liquid‐encapsulation Czochralski‐grown Fe‐ and Zn‐doped InP: A proof of the nonexistence of a Fe4+/Fe3+ donor level

Deep levels in liquid‐encapsulation Czochralski (LEC) grown p‐type InP:Fe codoped with Zn have been investigated by means of temperature‐dependent Hall‐effect (TDH), deep‐level transient spectroscopy (DLTS), calorimetric absorption spectroscopy, and electron spin resonance measurements. Although a dominant deep hole trap is revealed both by DLTS and TDH measurements in the vicinity of the valence band edge at EV+0.2 eV, the spectroscopic analysis unambiguously invalidates previous speculations on the existence of a second energy level of the isolated iron impurity in the band gap of InP, i.e., a Fe4+/Fe3+ donor level. From the axial concentration profile and a comparison with a LEC‐grown p‐type InP crystal doped with Zn only it seems that the trap is not even iron‐related in contrast to tentative assignments often found in the literature. Native or Zn‐related defects which depend on the particular growth conditions used are assumed to account for this level.

Transition metal doping of LP-MOCVD-grown InP

Abstract The growth of high-resistivity InP: Fe by LP-MOCVD is studied. The semi-insulating character of Fe-doped InP was found to vanish in contact with a p + -InP:Zn substrate. Ti-doping of InP is proposed as an alternative for the fabrication of semi-insulating material. Secondary ion mass spectroscopy is used to study the incorporation behavior of titanium in LP-MOCVD grown InP as a function of growth parameters. The optimum growth conditions to achieve abrupt titanium doping profiles are presented. In addition, first results on doping of InP with a 4d transition metal impurity are reported. The MOCVD growth of Zr-doped InP has been carried out using dimethylzircocene as organometallic source material.

Novel ways to grow thermally stable semi-insulating InP-based layers

Abstract Semi-insulating InP is generally grown by Fe doping. In contact with p-type layers, however, semi-insulating characteristics turn out to be difficult to reproduce because of pronounced interdiffusion of Fe and p-type dopants. Co-doping of InP:Fe with Ti is shown to be a universal process for the preparation of thermally stable high-resistivity layers. Fe + Ti co-doping can compensate both excess shallow donors and excess shallow acceptors up to concentrations of 8 × 10 16 and 2 × 10 16 cm -3 , respectively. In contrast to InP:Fe, resistivities in excess of 10 7 Ω cm are obtained in contact with both symmetric n- and p-type current injecting contacts. Moreover, co-doping of semi-insulating InP:Fe with Ti is found to suppress the interdiffusion of Fe and p-type dopants. Therefore, the out-diffusion and accumulation of Fe in other regions of complex device structures can be significantly reduced. A comprehensive model accounting for these phenomena is presented. A totally different way to produce thermally more stable semi-insulating InP layers is to replace Fe by a less diffusive deep acceptor. We propose the 4d transition metal Rh as a potential alternative. The diffusion of Rh is shown to be practically nonexistent and near-midgap Rh levels are found by means of DLTS in InP at E v + 730 meV and in InGaAs at E c - 380 meV below the conduction band. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.

Ion implantation of zirconium and hafnium in InP and GaAs

Abstract The redistribution of Zr and Hf implanted into InP and GaAs and the lattice recrystallization after annealing are studied. Zr and Hf profiles are measured by secondary ion mass spectroscopy. The recryslallization is evaluated by Rutherford backscattering/ channeling and X-ray double crystal diffractometry. After low dose implantation, both Zr and Hf show absolute thermal stability under standard heat treatments. Only after high dose implantation Zr is found to accumulate below the surface and to diffuse slowly into the bulk of InP and GaAs samples with a more pronounced redistribution in InP than in GaAs. Hafnium, in contrast, proves to be thermally stable even under extreme implantation and annealing conditions. A novel Zr-related level with an activation energy of (0.53±0.03) eV is identified in Zr doped n-InP:Si by deep level transient spectroscopy.

4He and 3He Calorimetric Absorption Spectroscopy: Principles and Results on InGaAs/AlInAs Quantum Wells and Fe in InP and GaAs

A novel absorption technique, Calorimetric Absorption Spectroscopy (CAS), is compared to other photothermally based spectroscopic methods. CAS is more sensitive than any other low-temperature absorption technique reported hitherto and it is quantitative. The method is based on the integral detection of phonons emitted during nonradiative recombination processes. A low-temperature resistance thermometer acts as phonon detector. The sensitivity of CAS increases drastically with decreasing temperature. An increase in sensitivity by an order of magnitude to 10 pW is reached by decreasing the base temperature from 1.3 K (4He-temperatures) to 0.5 K (3He-temperatures). Depending on the excitation density, αd products down to 10−10 can be detected. The experimental set-up to perform CAS measurements at 3He temperatures is described and modeled in detail. A direct determination of quantum efficiencies, obtained by combining CAS with calorimetric transmission spectroscopy (CTS), is demonstrated. Recent applications of CAS for the characterization of thin InGaAs/AlInAs quantum wells as well as for the study of the fine structure of deep traps like Fe centers in InP and GaAs are presented.

Semi-insulating InP codoped with Fe and Ti: An effective means to suppress the interdiffusion of Fe and p-type dopants

Codoping of InP:Fe with Ti was found to inhibit the pronounced interdiffusion of Fe and p-type dopants. Because of the high thermal stability and the simultaneous properties for excess shallow donors and excess shallow acceptors codoped InP:Fe+Ti remains semi-insulating in contact with symmetric n- and p-type current injecting contacts. In contrast to InP:Fe epitaxial layers, resistivities in excess of 10/sup 7/ /spl Omega/cm were obtained in both configurations. Details of the epitaxial growth procedure and of the electrical characteristics of InP:Fe+Ti are presented. The interdiffusion behavior of Fe and p-type dopants as well as its suppression by additional doping with Ti are explained by a comprehensive model.<<ETX>>

High-performance MSM photodetectors on semiinsulating InP:Fe/InGaAs:Fe/InP:Fe

The design, fabrication, and characterization of a novel type of InGaAs metal-semiconductor-metal (MSM) detector are reported. Based on an Fe-doped InGaAs layer and a 50-nm-thin Fe-doped InP cap layer which enhances the Schottky-barrier height, MSM detectors with low dark current of 15 nA at 5-V bias and a breakdown voltage of 25 V are realized. The high-speed characteristics are investigated by response measurements in the time and in the frequency domain. FWHMs (full widths at half maximum) of the impulse response of 17 ps and 13 ps are obtained under illumination with subpicosecond light pulses having wavelengths of 1.3 mu m and 0.62 mu m, respectively. Using the optical heterodyne technique at a wavelength of 1.3 mu m, the frequency response is investigated over a wide range of optical input powers (9 mu W-540 mu W) and bias voltages.<<ETX>>

A simple technique for simultaneous fabrication of p+/n diodes and ohmic contacts on n-type InP

Low leakage current p+/n step junctions with mechanically stable ohmic contacts to p+ layer are fabricated on n‐InP wafers simultaneously by a simple procedure consisting of vacuum evaporation of Ni, Zn, and Au followed by a short heat treatment at 340 °C. Current‐voltage and capacitance‐voltage measurements, secondary ion mass spectroscopy, and deep level transient spectroscopy are employed to characterize the diodes fabricated and to understand their structure.