Liquid phase epitaxial (LPE) grown junction In1−xGaxP (x∼0.63) laser of wavelength λ∼5900 Å...

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Liquid phase epitaxial (LPE) grown junction In1−x Ga x P (x0.63) laser of wavelength λ5900 Å (2.10 eV, 77°K) W. R. Hitchens, N. Holonyak Jr., M. H. Lee, J. C. Campbell, J. J. Coleman, W. O. Groves, and D. L. Keune Citation: Applied Physics Letters 25, 352 (1974); doi: 10.1063/1.1655505 View online: http://dx.doi.org/10.1063/1.1655505 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/25/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Narrow band gap (1eV) InGaAsSbN solar cells grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 100, 121120 (2012); 10.1063/1.3693160 15% efficiency (1 sun, air mass 1.5), largearea, 1.93 eV Al x Ga1−x As (x=0.37) np solar cell grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 52, 631 (1988); 10.1063/1.99387 Lowthreshold LPE In1−x′Ga x′P1−z′ As z′/In1−x Ga x P1−z As z /In1− x′ Ga x′P1−z′As z′ yellow double heterojunction laser diodes (J4 A/cm2, λ5850 Å, 77°K) Appl. Phys. Lett. 27, 245 (1975); 10.1063/1.88410 Liquid phase epitaxial In1−x Ga x P1−z As z /GaAs1−y P y quaternary (LPE)ternary (VPE) heterojunction lasers (x 0.70, z 0.01, y 0.40; λ Appl. Phys. Lett. 25, 725 (1974); 10.1063/1.1655377 Resonant enhancement of the recombination probability associated with isoelectronic trap states in semiconductor alloys: In1−x Ga x P:N laser operation (77 °K) in the yellowgreen (λ5560 Å ,ω2.23 eV ) J. Appl. Phys. 43, 5134 (1972); 10.1063/1.1661085 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 128.83.63.20 On: Wed, 26 Nov 2014 18:18:07

Transcript of Liquid phase epitaxial (LPE) grown junction In1−xGaxP (x∼0.63) laser of wavelength λ∼5900 Å...

Page 1: Liquid phase epitaxial (LPE) grown junction In1−xGaxP (x∼0.63) laser of wavelength λ∼5900 Å (2.10 eV, 77°K)

Liquid phase epitaxial (LPE) grown junction In1−x Ga x P (x0.63) laser ofwavelength λ5900 Å (2.10 eV, 77°K)W. R. Hitchens, N. Holonyak Jr., M. H. Lee, J. C. Campbell, J. J. Coleman, W. O. Groves, and D. L. Keune Citation: Applied Physics Letters 25, 352 (1974); doi: 10.1063/1.1655505 View online: http://dx.doi.org/10.1063/1.1655505 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/25/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Narrow band gap (1eV) InGaAsSbN solar cells grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 100, 121120 (2012); 10.1063/1.3693160 15% efficiency (1 sun, air mass 1.5), largearea, 1.93 eV Al x Ga1−x As (x=0.37) np solar cell grown bymetalorganic vapor phase epitaxy Appl. Phys. Lett. 52, 631 (1988); 10.1063/1.99387 Lowthreshold LPE In1−x′Ga x′P1−z′ As z′/In1−x Ga x P1−z As z /In1− x′ Ga x′P1−z′As z′ yellow doubleheterojunction laser diodes (J4 A/cm2, λ5850 Å, 77°K) Appl. Phys. Lett. 27, 245 (1975); 10.1063/1.88410 Liquid phase epitaxial In1−x Ga x P1−z As z /GaAs1−y P y quaternary (LPE)ternary (VPE) heterojunctionlasers (x 0.70, z 0.01, y 0.40; λ Appl. Phys. Lett. 25, 725 (1974); 10.1063/1.1655377 Resonant enhancement of the recombination probability associated with isoelectronic trap states insemiconductor alloys: In1−x Ga x P:N laser operation (77 °K) in the yellowgreen (λ5560 Å ,ω2.23 eV ) J. Appl. Phys. 43, 5134 (1972); 10.1063/1.1661085

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Page 2: Liquid phase epitaxial (LPE) grown junction In1−xGaxP (x∼0.63) laser of wavelength λ∼5900 Å (2.10 eV, 77°K)

Liquid phase epitaxial (LPE) grown junction In 1 -x Gax P (X"" 0.63) laser of wavelength A'" 5900 A (2.10 eV, 77°K)*

W. R. Hitchens, N. Holonyak Jr., M. H. Lee, J. C. CampbeW, and J. J. Coleman

Deparrment of Electrical Engineering and Materials Research Laboratory. University of Illinois at Urbana-Champaign. Urbana, Illinois 61801

W. O. Groves and D. L. Keune

Monsanto Company, St. Louis, Missouri 63166 (Received 21 May 1974; in final form 17 June 1974)

Laser operation (77 OK) of In1_xGaxP LPE p-n junctions is demonstrated at A~5900 A (2.10 eV, yellow). The junctions are prepared by the sequential growth (on GaAs1_yPy substrates) of first an n -type layer and then a Zn-doped p -type layer (not compensated). During growth of the p -type layer, Zn diffuses slightly (at reduced concentration) into the first layer, yielding a thin compensated active layer. The structure which results approximates in operation the behavior of a single heterojunction. Although the threshold for the laser operation of these devices is fairly high, it is demonstrated, nevertheless, that In1_x Gax P LPE grown junctions can be operated as lasers and, furthermore, at wavelengths A ;S; 5900 A.

Apart from one report of Zn-diffused In1_xGaxP (x - O. 27) laser junctions operating (77 OK) at A -7600 A (crystal grown at constant temperature from solution)l and a second report of vapor phase epitaxial (VPE) grown junction Inl_xGaxP (x - 0.57) lasers operating at A~6105 A (77 OK), 2 there has been no further report of the successful operation of a homo- or heterojunction laser in Inl_xG~P, not to mention at wavelengths shorter than 6000 A. Diode laser operation of In1_xGaxP has proven to be a notoriously difficult problem, probably, as we discuss elsewhere, 3 because of the large lattice mismatch between the two binary constituents InP (5.869 A) and GaP (5.451 A), the resulting need for careful control of the ternary crystal composition, the need for a good lattice match on any substrate crystal on which Inl_xG~P might be grown epitaxially, and probably also because of the peculiarities of impurity incorporation (impurity disturbances) in such a ternary Wide-gap system. For example, it is a simple matter to diffuse Zn into the n-type ternary GaAs1_xPx and make a junction laser, 4 but it is not so straightforward to ap­ply this Simple procedure to n-type Inl_xG~P, 1 which is otherwise known to be of laser quality5,6 and capable of photopumped pulsed laser operation even at room tem­perature. 7 Apparently Zn diffusion into Inl_xG~P can severely disturb the In-Ga sublattice. 4 Also, in spite of the fact that thin layers (- 1 J.!.) of x z O. 52 Inl_XG~P (doped or undoped) can be grown (LPE) between wider­gap n-type and p-type AlyGa1_yAs to form a double het­erojunction, this does not turn out to be an easily grown device, although in principle it should be possible to build. B Despite its intractable character, in this paper we describe the sequential LPE growth of two-layer homojunction Inl_xG~P (x - 0.63) lasers that operate (77 0 K) at a wavelength - 5900 A (yellow). The layer dopings are chosen to give an approximation to the carrier-confinement behavior of a single heterojunction. 9

Following a procedure described extensively recent­ly, 3,6 we grow first, by constant-temperature LPE (- 800 0 C, open tube furnace), a laser-quality n -type Inl_xG~P layer on a lattice-matched GaAs1_"Py substrate (x:::; O. 49y + 0.52). In the present work we have employed y '" O. 25 GaAs1_yPy substrates and grow x'" O. 63 Inl_xG~P.

352 Applied Physics Letters, Vol. 25, No.6, 15 September 1974

This chOice of substrate is somewhat arbitrary and can be higher in GaP concentration, permitting higher com­position Inl_xG~P to be grown. To grow the initial n­type layer, we employ a cylindrical graphite boat with removable end caps and a melt conSisting typically of 21 g of In, 0.48 g of InP, 0.23 g of GaP, and 10 mg of SeoThe melt is fir~t saturated at 800°C, then is cooled and the substrate crystal is placed off-center at one end. After reheating and a 5-10 °c cool down to effect supersaturation, the boat is rotated to permit the melt to contact the substrate and grow an n -type Inl_ .. G~P layer.

The ,layer is polished and etched, and the process is repeated with -100 mg of Zn replacing the Se doping. This results in the growth of an uncompensated p -type layer, with the melt serving also as a dilute Zn source permitting Zn diffusion into 1-2 J.!. of the initial n-type layer and thus creating a thin compensated layer-the active layer of the device.

A cleaved and etched cross section of the final struc­ture that results is shown in Fig. L The etchant used (for decoration) is similar to that mentioned previous­ly.5 Although it is not readily apparent in Fig. 1, under microscopic examination the compensated region, labeled p on, can be readily distinguished, Under photo­excitation this layer becomes strikingly apparent, If the cleaved surface is uniformly photoexcited by an Ar+ laser (77 0 K), the n- and p -Inl_xG~P layers glow (pale yellow) at nearly the same brightness and the thin p-n region appears as a bright layer shifted slightly in color toward the orange -yellow. If the Ar+ laser is focused to the limit as a probe excitation source, the n region exhibits a peak emiSSion at 2.159 eV, the p region at 2.130 eV, and thep-n region at 2.105 eV-and at 2x greater intensity than either the p or n regions. As the photoexcitation probe reveals, the empty donor band tail in the p -n region has the same effect as a reduction in bandgap in this region. Furthermore, the compensat­ed region clearly exhibits wave guiding effects. Photo­excitation of a spot on the p-n lasrer produces lumines­cence in the entire compensated layer, while neither of the adjacent layers is observed to glow. Thus, the

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L 1911

x '" 0.63 )' '" 0.25

FIG. 1. Cleaved and etched Fabry-Perot face of an In1_xGaxP p-n junction laser "grown by liquid phase epitaxy (LPE). The region labeledp-n is a thin (1-2 1') compensated (Zn-Se) layer formed when the p layer is grown (LPE) on the n layer. The circular mottled areas are due to etching and cannot be cor"­related with any crystal defects.

structure approximates a single heterojunction in behavior.

The LPE junction structure of Fig. 1 exhibits stimula­ted emission as shown by the spectral curves of Fig. 2, As expected, at low level the donor band tail of the p-n layer is not filled appreciably, and the emission peak occurs at relatively low energy (2.01 eV). This curve (102 A/cm2

) is shown dotted in Fig. 1; its intensity is actually lower than shown. At an excitation level of - 103 A/cm2

, the band filling is significant, and further excitation produces a relatively smaller shift in emis­sion. Beyond -104 A/cm2

, a certain fraction of the ex­perimental units exhibit noticeable line narrowing and at - 105 A/cm2 the narrow laser emission shown. This emission line occurs at an energy slightly below « 2. 105 eV) that of the photoexcited p -n layer region.

Some fine adjustments can be made to the LPE junc­tion growth procedure to reduce the high laser threshold that these devices exhibiL These adjustments include ensuring a perfect lattice match between the two epita­xial In1_xGaxP layers to minimize misfit defects in the junctions region and varying the width of the p -n layer to maximize the effects of its optical and carrier con­finements. Inhomogeneities in the Zn doping, which have been apparent in previous Zn-diffused Inl_xG~P, 3

must also be held to a minimum to ensure a uniform flat p -n region.

Demonstration of laser operation clearly shows that the LPE grown-junction material is useful in preparing laser junctions in the difficult In1_xGaxP system. Fur­thermore, the fabrication procedure is flexible and sufficiently well advanced to permit laser operation at the short wavelengths of 5900 'A (2.10 eV)o It is likely also that the crystal composition can be increased to x - O. 68 before the donor states associated with the X-

353 Appl. Phys. Lett .. Vol. 25, No.6, 15 September 1974

En~rgy (~V)

1n l _ x Gax P LPE Junction

\: '" 0.63

77 OK

6.4 6.2 6,(1

Wawkngtll (lOlA) 5.:\

FIG. 2. Electroluminescence spectra (77 OK) obtained on x '" 0.63 Inl_xGaxP laser diode. The p-n junction has been fabri­cated by successive LPE growth of n-type and p-type layers which are lattice matched to the y = 0.25 GaAs1-yPy substrate. The spontaneous spectrum, shown at the bottom of the figure, has been obtained by operating the diode at low injection lev­els. At higher excitation (~ 104 AI cm2) narrowing is observed, and laser operation is achieved at a current density approach­ing 105 Alcm2•

band minima cause a premature transition from direct to effectively indirect, which is a well known phenome­non in ternary III-Vs of this type. 10 This estimate of - 0.68 is simply determined from the relation

Er(x) = Ex!x) -EDX ,

where Er(x) are known experimental curves (discussed in Refs. 2,6, 11, and 12) and the donor energy associat­ed with the X indirect band edge is E DX -100 meV. Note that a further reduction is expected in the laser photon energy owing to the acceptor energy EA' Taking all these factors into account, including the diode laser data presented here, we estimate that it will be possible to operate (77 0 K)x - O. 68 Inl_xG~P as a junction laser at - 5700 'A (2.18 eV).

We are particularly grateful to Yuri S. Moroz and S. Moroz for technical assistance, and also to R. T. Gladin, J. Gray, K. Kuehl, and B. L. Marshall.

*Work supported by the National Science Foundation Grant No. GH-33771, the Advanced Research Projects Agency, Con­tract No. DAHC-15-73-G-10, and the U. S. Army Night Vision

tLaboratory, Contract No. DAAK-02-72-C0076. IBM Post-doctoral Fellow.

Hitchens et al. 353

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l H.M. Macksey, N. Holonyak, Jr., D.R. Scifres, R.D. Dupuis, and G. W. Zack, Appl. Phys. Lett. 19, 271 (1971).

2C.J. Nuese, A.G. Sigai, andJ.J. Gannon, Appl. Phys. Lett. 20, 431 (1972); C.J. Nuese, A.G. Sigai, M.S. Abrahams, and J.J. Gannon, J. Electrochem. Soc. 120, 956 (1973).

3W. R. Hitchens, N. Holonyak, Jr., M. H. Lee, and J. C. Campbell, J. Cryst. Growth (to be published).

4N. Holonyak, Jr. and S. F. Bevacqua, Appl. Phys. Lett. 1, 82 (1962).

5R. D. Burnham, N. Holonyak, Jr., D. L. Keune, and D. R. Scifres, Appl. Phys. Lett. 18, 160 (1971).

SH.M. Macksey, M.H. Lee, N. Holonyak, Jr., W.R. Hitchens, R. D. Dupuis, and J. C. Campbell, J. Appl. Phys. 44, 5035 (1973).

7J.C. Campbell,W.R. Hitchens, N. Holonyak, Jr., M.H. Lee, M. J. Ludowise, and J. J. Coleman, Appl. Phys. Lett. 24, 327 (1974).

8Zh. I. Alferov (private communication). 9Zh. I. Alferov, V. M. Andreev, V. I. Korol'kov, E. L. Portnoi, and D. N. Tret'yakov, Fiz. Tekh. Poluprov. 2, 1545 (1968) [Sov. Phys. -Semicond. 2, 1289 (1969»); I. Hayashi, M. B. Panish, and P. W. Foy, IEEE J. Quantum Electron. QE-5, 211 (1969); H. Kressel and H. Nelson, RCA Rev. 30, 106 (1969); R. D. Burnham, P. D. Dapkus, N. Holonyak, Jr., D. L. Keune, and H.R. Zwicker, Solid State Electron. 13, 199 (1970).

ION. Holonyak, Jr., C.J. Nuese, M.D. Sirkis, andG.E. Stillman, Appl. Phys. Lett. 8, 83 (1966); M. G. Craford, G.E. Stillman, J.A. Rossi, andN. Holonyak, Jr., Phys. Rev. 168, 867 (1968); A. Onton and R.J. Chicotka, Phys. Rev. B 4, 1847 (1971).

l1H.M. Macksey, N. Holonyak, Jr., R.D. Dupuis, J.C. Campbell, and G. W. Zack, J. Appl. Phys. 44, 1333 (1973).

12M. Altarelli (unpublished).

Microwave surface resistance of superconducting MOo.75Reo.25

J. A. Yasaitis* and R. M. Rose

Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 17 May 1974; in final form 5 July 1974)

A MOo.7sReo.2s alloy endplate was tested on a Nb TEoll mode microwave cavity resonant at 11.2 GHz. An upper bound for the surface resistance of 2.8 /Lfi and a lower bound of 102 G for the microwave magnetic breakdown field were established for the alloy plate. Comparison of these results to current requirements for a superconducting linear accelerator demonstrated the potential feasibility of this alloy as a practical alternative to Nb and Pb for accelerator applications. This is the first alloy shown to be a potential alternative to Nb and Pb and arguments are presented which indicate possible practical advantages of MOo.7sRea.2s over Nb and Pb.

In the development of superconducting microwave de­vices, notably high-energy linear accelerators, only the elements Nb and Pb have been extensively investi­gated. It is now apparent l - 4 that the achievement of stable low-loss rf properties with these materials will be difficult; the surface resistance and breakdown fields degrade, erratically and often drastically, with time, even with anodized Nb surfaces (which appear to be the most stable). On the other hand, alloys have received only limited attention, probably because of antiCipated difficulties in chemical homogeneity and surface prepa­ration, and because of the expectation that low losses would be attainable only in the Meissner state, 5 below He. However, recent developments6-8 suggest that He

1 rather than He may be the limiting magnetic field at

1 microwave frequencies. In addition, the interaction of Nb with oxygen, even in very small quantities, appears to create at least as many problems in preparation as a binary substitutional alloy.

As an interesting alternative, we have chosen to look at MoO.75Reo.25' for the following reasons: (a) high T e ,

- 10 OK, 9 to permit low theoretical losses at reasonable operating temperatures; (b) high He(O), -1600 Oe; (c) low K and hence relatively high H

e1, - 500 Oe 9; (d)

higher Re contents will increase Te but also lead to the presence of small inclusions of (normal) a phase 10;

(e) a minimum solubility for interstitials was predicted and confirmed for this composition. 11 Such behavior is

354 Applied Physics Letters, Vol. 25, No.6, 15 September 1974

expected in VI-VII tranSition metal alloys 12, 13 but not in alloys from groups IV and V. It is Significant in this connection that superconducting Mo-Re alloys appear to have highly reversible magnetic behavior9 without elaborate precaution (e. g., prolonged ultrahigh -vacuum annealing) .

We report here the first step in our evaluation of MOO.75Reo.25 as an X-band microwave material: We used it as an end plate in a two-piece TEo11 mode 11. 2-GHz cavity. The two pieces, a cylindrical cup and flat circu­lar endplate, were fabricated first from high-purity Nb which was machined, annealed, electropolished, 14 and anodized in 12.5% NH40H. (The details are too lengthy to set down in this paper.) Measurements were made on the cavity by the decrement method, with a Gunn diode source passively stabilized to the cavity resonance. A coupling coefficient (3 of 1. 6 or less was maintained throughout. High -power measurements were made with a TWT amplifier and a novel oscillator lOCking tech­nique which is described elsewhere. 15 After initial mea­surements were made on the all-Nb cavity, the Nb end­plate was replaced by one made of MOO.75Reo.25' The latter was made by arc melting, grinding, and electro­polishing. The final finish was shiny but visibly uneven.

The results are shown in Fig. 1, vs temperature from 4.2 to L 4 OK, for an incident power level of 18 mW. Even our rather modest residual Qo of 6x108 was not easy to attain; our experiences with other anodized

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