US A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2002/ A1 Sato (43) Pub. Date: Dec.

Transcription

1 US A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2002/ A1 Sato (43) Pub. Date: Dec. 26, 2002 (54) OPTICAL SEMICONDUCTOR DEVICE HAVING AN ACTIVE LAYER CONTAINING N (76) Inventor: Shunichi Sato, Miyagi (JP) (21) (22) (60) Correspondence Address: DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP 2101 L STREET NW WASHINGTON, DC (US) Appl. No.: 10/213,072 Filed: Aug. 7, 2002 Related US. Application Data Division of application No. 09/688,875,?led on Oct. 17, 2000, now Pat. No. 6,449,299, Which is a con tinuation of application No. 08/917,141,?led on Aug. 25, 1997, now Pat. No. 6,233,264. (30) Foreign Application Priority Data Aug. 27, 1996 (JP) Aug. 28, 1996 (JP) Sep. 5, 1996 (JP) Oct. 4, 1996 (JP) Oct. 4, 1996 (JP) Publication Classi?cation (51) Int. Cl H01L 27/15; H01L 31/12; H01L 33/00 (52) US. Cl /79 (57) ABSTRACT A laser diode includes a substrate, a lower cladding layer or a lower optical Waveguide layer substantially free from A1 and provided on the substrate, an active layer of a mixed crystal containing Ga and In as a group III element and N, As and/or P as a group V elernent, provided on the lower cladding layer; and an upper cladding layer or an upper optical Waveguide layer substantially free from A1 and provided on the active layer. RT units] [am OUTPUT LIGHT l ( I260 I270 I280 l 1 [ WAVELENGTH [nm]

2 Patent Application Publication Dec. 26, 2002 Sheet 1 0f 18 US 2002/ A1 FIG. I PRIOR ART 4.0 _--_- INDIRECT TRANSITION - GUN DIRECT-TRANSTITION A > 33 " A'F kq AlAs >_ O GGPO*T\ 2_ ED; AlSb LLI \ E \ ~O " GclnNAs \ gt _ LATTlCE-MATCHED~ 0 TO GGAs C] l q m _ l I 1.0 ~ I Ll.. l I.. l.. I.. I ' LATTICE CONSTANT (A)

3 Patent Application Publication Dec. 26, 2002 Sheet 2 0f 18 US 2002/ A1

4 Patent Application Publication Dec. 26, 2002 Sheet 3 0f 18 US 2002/ A1 PmD<IXm Z_ $8.43 m.@_u 0600 U w Q OQWO b PDO mmp<>> + mum 30m WEEK/Q0 AHU

5 Patent Application Publication Dec. 26, 2002 Sheet 4 0f 18 US 2002/ A1 m \\\\\\\\\\ \\\\ \.\ awiuosla b nm)\ c I NSF)! mqowlcumg m 4cm. 6E \\\\\\\\\\ \\\\\\\\\\\\

6 Patent Application Publication Dec. 26, 2002 Sheet 5 0f 18 US 2002/ A1 WAVELENGTH [nrn]

7 Patent Application Publication Dec. 26, 2002 Sheet 6 0f 18 US 2002/ A1 FIG. 6 I: 50mA ll76nm u) (0, INTENSITY 1l l1 800 I000 I200 I400 WAVELENGTH (nm)

8 Patent Application Publication Dec. 26, 2002 Sheet 7 0f 18 US 2002/ A1 Ml 20 Ill/Ill ll Ill/Ill FIG. 28 V273 V261 V251 iw24: \ 231 rv22 M M2 7 p* GcAs p - lngoasp InGoAsP InGoNAs ( QW) [HGCIASP : n InGGAsP ~2lzn-GOAs //// / ////// 29 FIG III/l / //l M /\/35 : V34 1 \/33 1 ~32; M2 p A GGAS InGGASP IHGCINAS (OW) InGuAsP n AIGcAs ~3l :n ~GGAS ///////////l l / 39

9 Patent Application Publication Dec. 26, 2002 Sheet 8 0f 18 US 2002/ A1 FlG. 9 [8 48 Ill/ll p+ - GclAs 46: 45: V44: "v43 InGoAsP InGo NA s (OW) InGoAs P n- In Go AIP M l will: n- GGAS /// / / 49 FIG.IO 58 Ill/Ill II I V57: p+ - GclAs w InGoAsP InGoNAs (OW) In GoAsP n-algoas ~5l: n GCIAS ////////l // 59

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12 Patent Application Publication Dec. 26, 2002 Sheet 11 0f 18 US 2002/ A1 A %<8 nmwz NE/ \\\\\\\\\\\1\\\\\\ \/i mm Om

13 Patent Application Publication Dec. 26, 2002 Sheet 12 0f 18 US 2002/ A1 M941 p InP,\,931 G0 InNAsP ///// // // f 97 I00 FIG. I5 I07 I p In GoAs Q6: p InP I05: GaInAsP _ ow GalnNAsP } 104- MQ BARRIER GoInAsP Ml I03: GaInAsP I02: n-inp M2 IOI :n-inp

14 Patent Application Publication Dec. 26, 2002 Sheet 13 0f 18 US 2002/ A1 FIG. I6A PRIOR ART InP CLAD Y ENERG GGlnASP BARRIER,GUIDE GclnAsP QW Fl 6. l 6 B I00 I06 r /\? '04 InP CLAD r /\ ERGY EN W GolnAsP BARRIER,GU\DE I02 GolnNAsP OW

15 Patent Application Publication Dec. 26, 2002 Sheet 14 0f 18 US 2002/ A1?mzmmmmmioov mqow CH1 15.: n7; us" \\

16 Patent Application Publication Dec. 26, 2002 Sheet 15 0f 18 US 2002/ A S m.. "8) :WS mn_ H W \\\ \ \\\

17 Patent Application Publication Dec. 26, 2002 Sheet 16 0f 18 US 2002/ A1

18 Patent Application Publication Dec. 26, 2002 Sheet 17 0f 18 US 2002/ A1 FIG. 20 I / IIII'IIII /\/ 3 8 (11/ 'P\" 3 7 \ / < 4 A~///////m ////////;»-B \ \ /////// ///////// / / //»\/39

19 Patent Application Publication Dec. 26, 2002 Sheet 18 0f 18 US 2002/ A1 FIG I42 I438 4 B A

20 US 2002/ A1 Dec. 26, 2002 OPTICAL SEMICONDUCTOR DEVICE HAVING AN ACTIVE LAYER CONTAINING N BACKGROUND OF THE INVENTION [0001] The present invention generally relates to optical semiconductor devices and more particularly to an optical semiconductor device for use in a 1.3 pm or 1.5 pm Wavelength band. [0002] Optical Wavelength band of 1.3 pm or 1.5 pm is used commonly in optical telecommunication systems that use optical?bers. It should be noted that a quartz glass optical?ber has an optical transmission band in the Wave length of 1.3 pm or 1.5 pm. [0003] In correspondence to the foregoing speci?c optical transmission band of the optical?bers, conventional optical telecommunication systems generally use a laser diode constructed on an InP substrate. Such a laser diode typically uses an active layer of InGaPAs having a lattice constant matching the lattice constant of the InP substrate and a bandgap corresponding to the optical Wavelength of 1.3 pm or 1.5 pm. [0004] While the foregoing laser diode that uses InGaAsP active layer performs Well in conventional optical telecom munication systems, particularly optical telecommunication trunks, the laser diode, requiring an expensive temperature regulation system such as a Peltier cooling device for a proper operation thereof, is deemed to be inappropriate for optical subscriber systems such as optical home terminals because of the increased cost of the temperature regulation system. In the foregoing laser diode that uses the InGaPAs active layer in combination With the InP substrate, the discontinuity of conduction band at the interface between the active layer and the surrounding cladding layer or optical Waveguide layer is not suf?cient for effective con?nement of the carriers in the active layer, and there is a tendency that the carriers escape or over?ow from the active layer When the device is not properly cooled. Because of such a poor con?nement of the carriers, the laser diode generally shows a poor ef?ciency of laser oscillation. This problem becomes particularly serious in a high temperature operation of the laser diode Where the carriers experience extensive thermal excitation. [0005] On the other hand, recent investigations on a GaAs GaN system have discovered that the bandgap of a GaAs mixed crystal containing therein a small amount of N decreases With increasing N content in the GaAs mixed crystal. GaN itself has been known to have a very large bandgap and is used for an active layer of an LED or laser diode that emits a blue or violet optical radiation. [0006] FIG.1 shows the bandgap of such a GaAs GaN mixed crystal system together With other group III-V com pound semiconductor materials (KondoW, M., et al., Extended Abstracts of the 1995 International Conference on Solid State Devices and Materials, Osaka, 1995, pp ). [0007] Referring to FIG.1, it should be noted that, While GaN or a mixed crystal thereof containing a small amount of As has a very large bandgap suitable for emission of blue or violet optical radiation, the mixed crystal of GaAs contain ing a small amount of N has a small bandgap suitable for emission of the 1.3 pm or 1.5 pm optical Wavelength band used for optical telecommunications systems. It should be noted that the bandgap of the GaAs mixed crystal decreases rapidly With increasing N content therein. Further, FIG. 1 indicates that the lattice constant of the GaAs mixed crystal decreases substantially With increasing N content therein. [0008] Thus, the Japanese Laid-Open Patent Publication describes a technology of growing a III-V mixed crystal?lm containing N on a Si substrate epitaxially. For example, the foregoing reference describes a laser diode and a photodiode that use a GaNP cladding layer having a composition of GaNO_O3PO_97 in combination With an active layer having a strained superlattice structure in Which a GaNP layer and a GaNAs layer are stacked alternately and repeatedly. The foregoing cladding layer successfully estab lishes a lattice matching With the Si substrate. According to the teaching of the foregoing reference, it becomes possible to form a III-V device on a Si substrate Without inducing mis?t dislocations in the epitaxial layers. Further, the dis closed technology enables formation of an integrated circuit in Which the III-V optical semiconductor devices are inte grated monolithically With other Si devices. [0009] Further, various mixed crystal compositions that establish a lattice matching With a substrate of GaAs, InP or GaP are reported for various N-containing III-V systems such as GaInNAs, AlGaNAs and GaNAs in the Japanese Laid-Open Patent Publications [0010] Conventionally, no III-V composition has been known that has a bandgap smaller than the bandgap of GaAs and simultaneously a lattice constant that matches the lattice constant of GaAs, until a mixed crystal of GaInNAs is discovered. Provided that the N content is held small, the GaInNAs mixed crystal successfully establishes a lattice matching With a GaAs substrate and simultaneously has a bandgap smaller than the bandgap of GaAs. See the band diagram of FIG. 1. Thus, the GaInNAs mixed crystal is thought to be a promising material for an active layer of an optical semiconductor device that operates in the 1.3 pm or 1.5 pm Wavelength band. HoWever, little is known about the properties of the mixed crystal of GaInNAs. [0011] Thus, KondoW, M., et al., op. cit., proposes a laser diode structure that uses a GaInNAs mixed crystal for the active layer of a laser diode. The reference further discloses the use of a cladding layer of AlGaAs in contact With the active layer of GaInNAs for securing a large discontinuity in the conduction band at the heterojunction interface across the cladding layer and the active layer. Because of the very large band discontinuity at the heterojunction interface, the laser diode is expected to show a high efficiency of laser oscillation and improved temperature characteristic associ ated With an ef?cient con?nement of the carriers in the active layer. [0012] On the other hand, It is known that the epitaxial growth of a GaInNAs mixed crystal is substantially difficult at high temperatures because of the tendency of the N atoms escaping from the deposited epitaxial layer of GaInNAs In order to obtain a?lm containing a substantial amount of N atoms, it is necessary to carry out the deposition process at a temperature of about 680 C. or less. HoWever, the epitaxial growth at such a low temperature is not preferable for the growth of a layer containing Al, such as a layer of AlGaAs used for the cladding layer, because of the tendency of the highly reactive Al atoms in the cladding layer reacting

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