1056 IEEE TRANSACTIONS ON ELECTRON DEVICES, NOVEMBER 1975

varied by three orders of magnitude. The product P o N ~ was approxi- mately the same at 2-20 W - cm-2.

Other device parameters also depend strongly on the dislocation density. The effects of dislocations on planarity of the junction front, threshold current density, reverse leakage current, injection effi- ciency, and quantum efficiency will be discussed.

We conclude that many properties of p-n junction lasers depend more strongly on the perfection of the starting material than on the process used to form the junction and that, when the fabrication process is optimized, impurity-diffused and self-diffused lasers are comparable in quality.

Session IIA

Lasers and LED’s

ITA-1 Composition Stabilization in GaAl As by Peltier-Induced LPE-J. J. Daniele, Philips Laboratories, Briarcliff Manor, N.Y 10510.

In normal liquid,phase epitaxial (LPE) growth of GaAlAs and ot,her ternaries, the composition of the solid varies as the crystai grows due to the necessary cooling and depletion of the melt. Usin$; Peltier-induced (current controlled) LPE1-3 a high degree of stabilization in the composition of the ternary solid has been achieved. Gal-,Al,As (0.1 5 z _< 0.3) epitaxial layers of 15-58-pnt thickness with a very uniform aluminum composition have bee11 grown in the temperature range between 600 and 850°C. The Peltier- induced LPE growth was carried out at constant temperature with d: as the sole driving force and controlling factor in the growth. Elec- tric current of 10-30 A/cm2 were passed through the S-L interface (which acts as the Peltier junction) thereby cooling this interfacs and causing growth (calculations show that other effects such as differential ion migration may also be present). In all cases, varia- tions of the aluminum concentration measured by photoluminescence microanalysis were observed to be f0.5 percent or less.

In addition t o the uniform composition, excellent electrical COT-

trol was achieved over the growth rate, which is linearly proportiond to the dc level. Growth rates of 0.12 to 0.85 rmlmin were observed.

Peltier-induced LPE of GaAlAs was also carried out for shol t intervals during normal (furnace cooling) LPE growth using dc of 20 to 30 A/cm2. A typical growth rate enhancement of six timw normal and a uniformity of aluminum composition of h0.5 perce1.t was observed in the Peltier-induced growth regions of the epi-layers.

p. 597, 1957.

J. Ekctrochem. Soc., vol. 120, p. 583, 1973.

and Related Compounds, Deauville, France, 1974.

1 W . G. Pfann, K. E. Benson, and J. H. Wernick, J. Electron., vol. .1.

131. Kumagawa, A. F. Witt, ?VI. Lichtensteiger, and H. C. Gatos,

3 J. J. Daniele and C. Michel, presented at the 5th Int. Symp. Gafis

IIA-2 Loss Mechanisms in GaAlAs Electroabsorption Light Modulators-J. C. Dyment and F. P. Kapron, Bell-Northern.Rs- search, Ottawa, Ont. Canada.

Electroabsorption (EA) light modulators formed from reverse- biased GaAlAs double heterostructures have been studied in bo;,h discrete’ and integrated2 optoelectronic structures. Although hig:h extinction ratios (? 30 dB/O.g-mm length) were measured, little w ts known about those loss mechanisms which ultimately limit mod+

terization of electroabsorptlon modulation in reverse-biased GaAlAs 13. C. Dyment, F. P. Kapron, and A. J. Spring-Thorpe, “Charac-

double heterostructures,” DRC. paper IV-6, Santa Barbara, CaliP.. June 25-27, 1974. Abstract published in IEEE Trans. Electron Devicls, V O l . ED-21, p. 742, h-0~. 1974.

verse-biased GaAs-GaAIAs double heterostructures,” presented at tne

lished in Conference Series 24, Brit. Inst. of Physics, 1975. 5th Int. Conf. GaAs, Deauville, France, Sept. 24-26, 1974; to be pub-

2- , “The devices based on electroabsorption (EA) effects in re-

lator performance. This paper reports results of experimental measurements and theoretical analysis of the role of absorption and scattering losses in modulator performance. Scattering losses, which have not been previously studied in these devices, arise from bulk and interfacial imperfections which are introduced during crystal growth or fabrication procedures.

A phenomenological theory has been developed which assumes that the modulator is divided into two regions. Region (1) contains the guiding layer which is characterized by a voltage-dependent EA absorption loss and a voltage-independent scattering loss. Region (2) consists of both outside confining layers which are characterized by voltage-independent absorption and scattering losses.

We show that light scattered from region (2) into region (1) plays an important role in modulator performance. If “a” i s the EA co- efficient and “1” the modulator length, this mechanism results in a small background level in the detected light which decreases as a-1 for sufficiently large a1 product rather than as more usual exp (-aZ) for smaller al. In order to study these phenomena, a new multiple modulator structure was designed. It is comprised of four individual modulator elements, each of different lengths (from 150 to 600 pm) on the same chip. For wavelengths sufficiently above the absorption edge, the transmitted light level exceeded the background light level for all voltages and hence the extinction ratios (in dB) were propor- tional to the modulator lengths. On the other hand, for wavelengths closer to the edge, length normalization did not occur; the EA effect in the longest modulator was limited by background light whereas the light transmitted through the shortest.modulator continued to de- crease with increasing bias.

By varying the relative positions of both the input light and detector within regions (1) and ( Z ) , data has been obtained con- cerning the spatial distribution of scattering centers. Most modula- tors show a large increase in the density of scatter centers at a distance of 2-3 pm into the n-GaAlAs confining layer. The theory has provided good qualitative agreement with the experimental data.

IIA-3 Buried Etched Striped Substrate Heterostructure Laser- R . D. Burnham and D. R. Scifres, Xerox Corporation, Palo Alto Research Center, Palo Alto, Calif. 94304.

A different type of buried stripe geometry diode laser1 is demon- strated in which current and wave confinement are achieved by sur- rounding a “semi-circular” shaped p-GaAs active region with p and n-type Gao.,Alo.sAs. These devices are fabricated by very simple techniques which involve 1) Zn surface diffusion of an entire n- GaAs substrate, 2) selective etching of narrow (-3-pm) grooves which are deeper than the surface diffusion layer, 3) growth by liquid phase epitaxy in the substrate grooves which results in the formation of the “semi-circular” buried active regions. These lasers have been operated a t current levels as low as 120-mA for a 375-pm-long diode. The far field radiation pattern of these lasers is more symmetric (-50” X 70” at the half power points) than that of conventional stripe geometry lasers owing to the more symmetric dimensions of the active region. It is believed that these lasers are capable of much lower room temperature threshold currents than has been achieved to date if leakage currents through the Zn-diffused substrate region can be eliminated. Aspects of liquid-phase epitaxial growth required for fabrication of this structure and possible methods for reduction of leakage currents will be discussed in detail.

1 T. Tsukada. J. A p p l . Phys. . vol. 45, p. 4989, 1974.

IIA-4 Low Threshold LPE Inl~~~,Ga2~,P1~,~ ,As~~, / Inl ,Ga,P1~,As , / , Inl_,~,Ga,,P1_,~,As,~, Yell$w Double Heterojunction Laser Diode? (J < 104A/cm2, X = 5850 A, 77’K)13-W. R. Hitchens, N. Holonyak,! Jr., P. D. Wright and J. J. Coleman, Dept. of Electrical Engineering and Materials Research Laboratory, University af.Illinois a t Urbana- Champaign, Urbana, 111. 61801.

1 This work has been supported by the National Science Foundation, Grant DMR-72-03045-A01, and the Advanced Research Projects Agency, Contract DAHC-15-73-G-10.

9 Abstract for consideration of 1975 IEEE DRC.

DEVICE RESEARCH CONFERENCE 1057

For some time it has seemed likely that the quaternary In]-=- Ga,P1-,As,, which is a direct-gap material extending from the yellow-green to the infrared, might be a better choice of alloy 111-V semiconductor to employ for high-energy laser emission (yellow) than Inl-,Ga,P. This possibility is inherent in the fact that any increase Ax in Ga composition x that shrinks the crystal lattice can be balanced by a corresponding increase Az in As composition z that increases the lattice constant, thus leading to a fixed lattice constant and above all a mechanism to minimize lattice defects and strains. Utilizing these notions and the usual slider-boat LPE crystal growth process, we have fabricated In,_z’Ga~’PI-E’Asl’/Inl-=Ga~Pl-~As~/ Inl-Z’Ga,’Pl-.z’Asz’ (x’ - 0.66,~’ - 0.005;~ - 0.71,~ - 0.10) double heterojunction laser diodes that operaie in the yellow a t cur- rent densities (J < lo4 A/cm2,X - 5850 A,77 K) an order of mag- nitude lower than comparable Inl-,Ga,P homojunctions. In this report we describe the lattice-matched LPE quaternary growth process and the quaternary double heterojunction laser diodes and their properties.

IIA-5 Efficient Gaftsl-,Sb,/AI,Gal-,Asl-,Sb, Double Hetero- structure LEDs in the 1-pm Wavelength-Region-R. E. Kahory, M. A. Pollack, E. D. Beebe and J. C. DeWinter, Bell Laboratories, Holmdel, N.J. 07733.

We report the liquid-phase expitaxial (LPE) growth, fabrication and operation of efficient double-heterostructure (DH) light emitting diodes (LED’s) based on the GaAsl_,Sb,/Al,Gal_,Asl-,Sb, alloy

These devices emit in the region of lowest loss of optical fiber transmission, lines, a t wavelengths around 1 pm and beyond. Similar D H GaAs/AlGaAs LEDs have received attention re- cently4J as possible sources for fiber systeriis, but at wavelengths in the more lossy 0.8-0.9-pm region.

The LED reported here consists of six epitaxial layers grown by LPE on a [loo], Sn-doped GaAs substrate. Three layers of GaAsl-,- Sb,, with x = 0.025, 0.058, and 0.093, are used between the sub- strate and subsequent layers to provide stepwise compositional grading.6 The recombination region of the structure is a layer of GaAsl,Sb,:Ge (x =. 0.12) sandwiched between p- and n-type cladding layers of Al,Gal-,Asl-,Sb, (x = 0.12 ,~ = 0.17) to provide confinement. For purposes of comparison, GaAsl-,Sb, homojunction diodes (x = 0.12) were also grown using the same LPE growth system.

Junction edge electroluminescence spectra of the homojunctions peak a t 1.04 pm. and have a FWHM of 0.06 pm. The external quan- tum efficiency is -0.12 percent. For the double heterostructures the spectra are narrower, FWHM as small as 0.043 pm, and peak at -1.00 pm. This wavelength differs from that of the homojunctions because of the carryover of a small amount of AI from the n- AlGaAsSb solWcion during the growth process. The external quantum efficiency achieved for the DH LEDs is 2.1 percent. This corresponds to a power efficiency of 1.9 percent, a t a pulsed current level of 0.2 A.

Although the :parameters have not yet been completely optimized for these D H LED’s, their excellent efficiency in the 1-pm wave- length region makes them strong candidates for use with fiber trans- mission lines.

1970. 1 G. A. Antypas and L. W. James, J. A p p l . P h y s . , vol. 41, p. 2165,

2 K. Sugiyama and H. Saito. J a p a n J . A p p l . P h y s . , vol. 11, p. 1057,

a G. A. Antypas and R. L. Moon, J. Electrochem. Soc., vol. 121, p. 416,

M. Ettenberg, H. F. Lockwood, J. P. Wittke, and H. Kressel, 4 C . A. Burrus and B. I . Miller, Optics C o m m u n . , vol. 4, p. 307, 1971.

6 R. E. Nahory, M . A. Pollack, and J. C . DeWinter, A p p l . P h y s .

1972.

1974.

I E D M T e c h . D i g . , p. 317, 1973.

Let t . , vol. 25, p. 146, 1974.

IIA-6 Graded Gap Diodes-Increasing the Efficiency of p-n Junc- tion Zinc Sulfo-selenide LED’s-R. J. Robinson, T. Martin, and E. Maryniak, Zenith Radio Corp., Chicago, Ill. 60639.

A technique has recently been discussed’ by one of us for generating a t least lo1’ holes/cm3 at room temperature in zinc selenide and zinc sulfoselenide from a new type of shallow acceptor level. p-n junction LED’s are made by diffusing selected Group IIIa elements (in the presence of zinc) into n-type selenide and zinc sulfo-selenide sub- strat,es. Light, however, is generated only on the n-side of the LED; hence only the holes are useful as minority carriers. The p-n junction is placed in a graded-bandgap layer to enhance hole injection: this is necessary because hole mobilities are very low compared to that of electrons. This has resulted in LED efficiencies above one percent. The graded-bandgap layer is produced by low temperature vapor phase epitaxy followed by heating. The technique and efficiency results will be discussed.

1 Presented at Special is t Conf . on ~ Technology of Electroluminescent Diodes, Atlanta, Ga., Nov. 20-21, 1974. Submitted for publication A p p l . P h y s . L e t t .

ITA-7 Guided-Light Beam Deflection/Switching and Modulation Using Tilted-Electrode Structures in LiNb03 Waveguides-C. S. Tsai and P. Saunier, Department of Electrical Engineering, Carnegie- Mellon University, Pittsburgh, Pa. 15213.

Theoretical and experimental. results on new guided-wave electro- optic devices for ultrafast optical deflection, switching and modula- tion are presented. The devices utilize simple electrode arrangements consisting of a small number of tilted electrodes which effectively simulate prism structures in electrooptic waveguides. Devices using single-mode Y-cut LiNb03 out-diffused waveguides have demon- strated excellent performance figures: nine beam positions (channels) per unit at a driving voltage of 8 V per beam posit,ion, 0.5 dB optical insertion loss, and crosstalks between adjacent channels varying from -13.5 to -9 dB. The new devices are shown to be capable of per- forming optical multiport beam deflection/switching and modulation a t very low driving voltages and at ultrafast speeds because of their very small capacitances, and are, therefore, highly useful for future wideband fiber and integrated optic systems.

Session IIB

Charge-Coupled Devices

IIB-1 Noise Measurements on Buried-Channel Charge-Coupled Devices-R. W. Brodersen and S. P. Emmons, Texas Instruments Incorporated, Dallas, Tex. 75222.

For the first time, measurements of bulk state trapping noise will be reported. These measurements were made on linear 150 stage buried-channel charge-coupled devices (BCCD’s). The t,otal device noise was found to be composed of three components; the electrical insertion of signal charge, bulk state trapping, and the output am- plifier. We did not observe any of the extraneous parasitic noise sources such as pulser noise and abnormally high input noise which have been observed by previous authors.ls2

In making t.hese measurements the concept of correlated double sampling3 was used in an output amplifier which had a noise level which was equivalent to less than 30 noise. electrons. The dominant noise contributors in this amplifier will be discussed.

A low noise input structure for electrical insertion of signal charge was used which introduced a noise equivalent to less than 40 e-. A description of this input will be given as well as an analysis of its operation.

The extremely low noise levels just described which were obtained at the input and output have made possible direct measurement of

vices,” R C A Rev., vol. 34, Dec. 1973, p. 553. 1 J. E. Carnes et al., “Measurements of noise in charge-coupled de-

Performance of bulk channel charge-coupled devices,” I E E E T r a n s . * A. M. Mohsen and M. F. Tompsett, “The effect of the device on the

Electron Devices, vol. ED-21, pp. 701-711, Nov. 1974. a M. H. White 61 ai., “Characterization of surface channel CCD image

arrays a t low light levels,” IEEE J. SoEid-State Circuits. vol. SO-9, pp. 1-10, Feb. 1974.