L.J. Balk

Two-dimensional field mapping in MMIC-substrates by electro-optic sampling technique

A system for two-dimensional field mapping in MMIC (monolithic microwave integrated circuit) substrates using direct electrooptic sampling is introduced. Measurements up to 8.5 GHz have been made. The main application of the field mapping technique is the analysis of complex MMICs. The proposed test technique is characterized by the fact that, due to the small laser beam, a high spatial resolution and a high temporal resolution (<5 ps) can be reached, allowing testing in a contactless and noninvasive manner. It offers a quick survey of the actual internal field distributions, thus making control of the simulation procedure possible. It is evident that by these means easy failure and function analysis within a MMIC can be achieved, leading to significant reduction of the otherwise time-consuming design/redesign loop.<<ETX>>

Electron beam testing of monolithic integrated micro- and millimeterwave circuits

Abstract An electron beam testing system has been developed, consisting of a new type of electron beam blanking system and a specimen holder designed for applying GHz-frequencies to the device under test. First quantitative measurements have been done on a special test structure, showing the influence of the transit-time-effect on quantitative measurements. These experimental results were compared with results obtained by simulations, showing good agreement. Although the electron beam testing system works in a frequency range from 8 to 18 GHz the results show that quantitative measurements are only practical for frequencies below 2.5 GHz, assuming a maximum measurement error of 10%.

Microcharacterization of electroluminescent diodes with the scanning electron microscope (SEM)

A complete material characterization of electroluminescent diodes necessarily requires a high spatial resolution because of the micron-sized thickness of the different epitaxial layers. A modified arrangement of a scanning electron microscope (SEM) has proven to be an extremely useful tool for obtaining information on the various parameters of each of these layers. It will be shown that the analysis of the electron beam induced voltages (EBIV) and currents (EBIC) allows not only the location of the junction itself, but also the detection of all other built-in barriers. Measurements of the EBIC permit separation of barriers less than 1 µm apart; even barriers in a direction oposite to that of the junction are detected in this manner. The peak value of EBIC is largely independent of the barrier height, but it is sensitive to variations in the concentration of the components of the lattice. Because of the exponential decrease of EBIC with the distance between primary electron beam and barrier, the minority carrier diffusion length can be obtained for all different barriers. The height of barriers, 2.5 µm separated and with the same direction as the p-n junction, can be determined quantitatively by the maximum of EBIV. By measurement of the cathodoluminescence (CL) signal regions of different recombination probabilities for radiative transitions (and therefore different luminescence yields) can be distinguished. Thus inhomogeneities of the structure can be detected. By spectral CL analysis the spatial variation of the width of the bandgap will be shown.

A 100-femtosecond electron beam blanking system

Abstract Conventional electron beam blanking system show the drawbacks of a fixed electron energy, a fixed repetition rate or even unsuitability for repetition rates in the GHz region. This paper describes the development of an ultrafast electron beam blanking system, intended for testing microwave integrated circuits with very high temporal resolution. 100fs electron pulses can be generated with repetition rates in the range from 8 to 18 GHz.

Evaluation of dynamic magnetic stray fields with high spatial and temporal resolution

A setup has been realized for determination of magnetic field distributions with 50‐nm spatial resolution and temporal resolution of <1 ns. For typical device configurations the system has a sensitivity of about 1 mT. Important system features are use of stroboscopic techniques; sine wave or pulsed operation of the magnetic device from 100 Hz to 60 MHz; precise determination of the distance between measuring position and head surface; and determination of the electron beam waveform by streak‐camera technique with a temporal resolution of 50 ps, even for beam currents of <1 fA. This setup has been applied to the examination of thin film magnetic heads with a 0.6‐μm gap and a track width of 26 μm.

Orientation dependent growth and luminescence of selective GaAs-Sn LPE

Abstract Heavily Sn doped selective structures were grown by GaAs liquid phase epitaxy (LPE) both into circular holes and into 〈011〉 orientated stripes. An orientation dependent edge overgrowth of the original etched hole with the preferred directions 〈100〉, 〈111〉 and 〈110〉 was observed. It is shown that the kinetic processes, becoming visible with selective epitaxy only, are compatible with the well known diffusion controlled growth in the case of layer growth. An epitaxial mesa structure with completely smooth surfaces suitable for practical applications is reported. Scanning photo- and cathodo-luminescence measurements were carried out. A luminescence intensify profile influenced by the different preferred directions was found. The different luminescence intensities are interpreted as being caused by different doping concentrations. This interpretation is confirmed by the peak energy position and the half-width of luminescence bands. A donor concentration ratio of N D100 : N D111 : N D110 ≌1:0.85:0.7 has been found.

Time resolved cathodoluminescence in the scanning electron microscope by use of the streak technique

Minority carrier lifetime is one of the basic material properties in optoelectronic devices and material. Both the micrometer range dimensions of the devices and lifetime variations around defects in materials require a lifetime measurement technique with both high spatial and high temporal resolution. In order to meet these requirements a highly efficient cathodoluminescence (CL) measurement system has been developed consisting of a commercial scanning electron microscope extended for integral and spectral CL‐measurements and a streak camera with subnanosecond time resolution as time resolving detector. The lifetime is determined by evaluation of CL‐decay time after excitation of the specimen by an electron beam pulse, which is blanked in less than 50 ps by an adjustable plate capacitor. The CL‐light is collected by an adjustable, ellipsoidal mirror and can be dispersed in a vacuum monochromator. The monochromator exit slit is imaged on to the photocathode of the streak camera, which transforms the temporal distribution of the photon intensity into a lateral distribution on the camera phosphor screen after amplification by an integrated microchannel plate. By this technique it is possible to record the complete CL‐decay simultaneously, thus avoiding all measurement falsifications by system instabilities. The resulting intensity distribution is read out by a SIT vidicon camera with subsequent multichannel analyser, providing an intensity plot versus streak time in less then 1 min for each beam spot location. The technique is therefore well suited for lifetime mapping experiments. The best time resolution of the complete system achieved today is about 100 ps. Its performance is here demonstrated by measurements of the temperature dependence of the CL‐decay in a highly Se‐doped GaAs specimen in the temperature range from 90 K to 300 K.

Capacitive Transducers for Scanning Electron Acoustic Microscopy (SEAM)

In scanning electron acoustic microscopy piezoelectric transducers, mainly based on PZT ceramics, are used for picking up the sound signal as generated due to electron impact within a specimen. The acoustic contact between sample and transducer is achieved either by glueing or by mechanical force. Though this technique delivers high detection efficiencies it has various drawbacks. One of these is due to the necessary mechanical contact possibly causing signal artefacts, especially for thermally thin samples, the other one the inability to carry out wide—range temperature dependent measurements, as the usability of piezoelectric ceramics is limited by their Curie temperature and as their transducing efficiency changes with temperature. To overcome these shortcomings, capacitive transducers which do not imply material properties and which do not need mechanical contact with the sample may be applied.

An Improved Measurement System for the Investigation of Sensitive Specimens by Means of Scanning Electron Acoustic Microscopy (SEAM)

In contrast to other modes of Scanning Electron Microscopy (SEM) SEAM usually necessitates high electron beam currents to achieve a sufficient signal—to—noise ratio. In addition, for taking a SEAM—micrograph being the main use of this method in order to detect specimen inhomogeneities, high irradiation times of the specimen are necessary. Due to the fact that specimens are thermally, mechanically, and electrically loaded a damage of sensitive specimens like semiconductor devices or plastic materials cannot be excluded. In order to reduce the radiation dose an improvement of both the detection technique and the signal acquisition is necessary.

Signal Generation and Contrast Mechanisms in Electron and Photo Acoustic Imaging of Differently Doped Silicon

Applicability of electron and photo acoustic imaging to the evaluation of material properties is governed by the exact knowledge of signal generation and contrasts mechanisms. Whereas this seems to be given sufficiently well for metals, the understanding for silicon has been still unclear. Based on theoretical models and on crucial experiments this paper clarifies this situation.