IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-33, NO. 11, NOVEMBER 1986 1859

VA-8 CW Operat ion of GaInAsSb/AIGaAsSb DH Lasers-C. Caneau, A. K. Srivastava,* J. L. Zyskind, J. W. Sulhoff, A. G. Dentai, and M. A. Pollack, AT&T Bell Laboratories, Holmdel, NJ 07733.

Semiconductor lasers operating CW at wavelengths in the 2-4 pm region will be required for future mid-IR communication sys- tems which are predicted to have extremely low transmission losses. Gal _Jn,As,Sb1 -, alloys lattice matched to GaSb (with y/x = 0.9) seem well suited for such lasers because they span the range from 1.7 to 4.3 pm. Recently, room-temperature pulsed operation of GaInAsSb/AlGaAsSb DH lasers has been reported [ 11, [2] at wave- lengths of 2.2 to 2.3 pm, but CW operation has only been achieved at 80 K [3]. Here we present the characteristics of such lasers ca- pable of CW operation at significantly higher temperatures.

The laser structures consist of GaInAsSb (bandgap X - 2.1 pm) active layer and AlGaAsSb confinement layers grown by LPE at 530°C on (100)GaSb : Te substrates. The grown layers were closely ( A d a 5 lattice matched to the GaSb substrate. Unintention- ally doped GaInAsSb and AlGaAsSb layers were p-type with p - 2 X l O I 7 ~ m - ~ ) . Tellurium was used as a dopant in the n-confine- ment layers. The grown wafers were processed into broad area (stripe width S = 75 pm) and small-area (S = 9 and 14 pm) stripe lasers using standard photolithographic techniques. Silicon nitride provided the electrical isolation; the ohmic contacts to the n- and p-sides were made by alloying Au-In and Au-In-Zn, respectively.

Broad area lasers with active layer thickness between 0.2 and 1.5 pm were characterized for pulsed operation using a cooled InSb detector. The lowest threshold current density at room temperature (4 kA/cm2) was obtained for lasers having active layer thicknesses of about 0.8 pm. The peak wavelength and the characteristic tem- perature To were measured to be 2.2 pm and 80 K, respectively. Narrow-stripe lasers showed CW lasing in several well-defined Fa- bry-Perot modes up to 220 K with threshold currents of 130 to 150 mA. This is the highest temperature CW operation reported for diode lasers at these wavelengths, and modest reduction of series resistance and threshold current should permit CW operation at room temperature.

*On leave from the Tata Institute of Fundamental Research, Bombay, India. [l] C. Caneau, A. K. Srivastava, A. G. Dentai, J . L. Zyskind, and M . A.

PollackElectron. Lett., vol. 21, p. 815, 1985. [2] A. E. Bochkarev, L. M. Dolginov, A. E. Drakin, L. V . Druzhinina,

P. G. Eliseev and B. N . Sverdlow, Kvantovaya Elektron. (Moscow), vol. 12, p. 1309, 1985.

[3] H. Kano and K. K. Sugiyama, Electron. Lett., vol. 16, p. 146, 1980.

VB-1 Photoelectron Sampling of Waveforms for High-speed Testing-R. B. Marcus,* A. M. Weiner,** J . H. Abeles,* and P. S . D. Lin,** *Bellcore Labs, Murray Hill, NJ, **Bellcore Labs, Holmdel, NJ.

80-fs laser pulses are used to generate photoelectrons from a metal line carrying a high-speed signal on a GaAs or silicon device or circuit; the photoelectron spectrum is then measured in order to derive the potential of the waveform at the time of emission.

Contactless testing of integrated circuits by spectral analysis of secondary electrons stimulated by electron bombardment appears to be limited to electron-beam probe pulses longer than 0.1 ns [ l ] , [2], and is therefore inapplicable for analysis of high-speed wave- forms. Optoelectronic probing [3], [4], which measures the effect of the electric field created by a signal on the polarization of a pulsed laser beam as it transmits through an electrooptically active device, requires a restrictive sample geometry, and is not suitable for devices on nonelectrooptically active material (e.g., silicon).

Our method uses a two-electrode analyzeddetector to analyze the photoelectrons generated by three-photon absorption. A collid- ing-pulse mode-locked dye laser generating 80-fs pulses at 625 nm was focussed to a small spot (< 2 pm) on a gold transmission line

on GaAs carrying either a static voltage or a pulsed signal. Static measurements show the expected third power dependence of pho- toelectron current on optical intensity, and demonstrate a lo4-fold increase in current from a roughened surface. Time-resolved mea- surements on 650 and 90 ps electrical pulses demonstrate an elec- tron transit time limitation to analysis of the fas,ter pulse imposed by the geometry of the analyzer.

With proper analyzer geometry, this approach to waveform mea- surement is expected to be-useful for measurernent of signals as fast as 1 ps.

[l] E. Wolfgang, R. Lindner, P. Fazekas, and H. P. Feuerbaum, IEEE J .

[2] E. Menzel and E. Kubalek, Scanning, vol. 5, pp. 103-122, 1983. [3] J . A . Valdmanis, G. Morou and C. W., Gabel, Alppl. Phys. Lett., vol.

[4] B. H. Kolner and D. M. Bloom, Electron. Lett., vol. 20, p. 818, 1984.

Solid State Circuits, vol. SC-14, pp. 471-481, 1979.

20, p. 818, 1984.

VB-2 Laser-Induced Photoemission for Contactless High- Speed IC Testing-A. Blacha, R. Clauberg, H . K. Seitz, and H. Beha, IBM Zurich Research Laboratory, CH-8803 Ruschlikon, Switzerland.

A new method for contactless testing of integrated circuits and devices has been invented recently [l] . In this novel, so-called in- tegrated circuit laser testing (ICLT) approach [I.], short laser pulses in the ultraviolet (exceeding the threshold for photoemission, Le., >4 .5 eV for metals) are used for contactless measuring of voltages and waveforms on metallic lines of semiconductor devices. The voltage value is extracted from the energy distribution of electrons photoexcited by the laser pulses. Our method allows a spatial res- olution in the submicrometer range given by the diffraction limit for UV photons and a time resolution given lby the width of the laser pulses and the electron transit-time effect [2]. Also, it is ap- plicable to silicon-based technologies as well as GaAs. These are important advantages for the measurement of voltages and wave- forms in high-speed and very large scale integrated circuits com- pared to the known existing methods of contactless testing, such as e-beam and electrooptic sampling.

The e-beam method uses the analysis of secondary electrons after electron beam excitation, while the electrooptic sampling method exploits the effect of electric fields on the polarizaltion of laser pulses [3]. The disadvantage of the e-beam method is the large measuring time required for high time resolution in cornbination with high spatial or high voltage resolution. Electrooptic sampling methods, are restricted to electrooptically active materials like GaAs, but are not applicable to silicon-based technologies, since silicon is not electrooptically active. They also require a special geometry and are limited practically to a spatial resolution of about 2 pm, since the photon energy may not exceed the energy galp of the electroopt- ically active material.

We achieved the first experimental results, confirming the fea- sibility of the novel ICLT approach, by using a special laser system [4]. This system produces 1.5-ps laser pulses at 2.5-eV photon en- ergy, which are then converted into pulses of 5-eV photon energy by second-harmonic generation. The photoelecton detector con- tains an accelerating grid to extract the electrons from the sample. This grid is needed to overcome the problem of microfields and to reduce the transit-time effect which limits the time resolution. With this set up the first experiments achieved already a dc voltage res- olution better than 50 mV for an air-exposed sample of A1 on Si. Real-time measurements are performed with a feedback loop which adjusts the retarding voltage to keep the photoelectron current con- stant. For ultrafast signals a stroboscopic sampling method has to be applied.

This method has the potential for becoming a major tool in con- tactless testing of VLSI and VHSI circuits.

[ l] H. Beha, R. W. Dreyfus, and G. W. Rubloff, 1J.S. patent (pending).