Spatially resolved observation of carrier leakage in 1.3μm In1−x Ga x As y P1−y lasersLiangHui Chen, J. C. V. Mattos, F. C. Prince, and N. B. Patel Citation: Applied Physics Letters 44, 520 (1984); doi: 10.1063/1.94818 View online: http://dx.doi.org/10.1063/1.94818 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/44/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Suppression of electron and hole leakage in 1.3 μm AlGaInAs/InP quantum well lasers using multiquantumbarrier Appl. Phys. Lett. 72, 2090 (1998); 10.1063/1.121285 On the hotcarrier effects in 1.3 μm InGaAsP diodes J. Appl. Phys. 73, 7978 (1993); 10.1063/1.353909 Temperature dependence of carrier lifetime and Auger recombination in 1.3 μm InGaAsP J. Appl. Phys. 57, 5443 (1985); 10.1063/1.334820 Photoexcited carrier lifetime and Auger recombination in 1.3μm InGaAsP Appl. Phys. Lett. 42, 259 (1983); 10.1063/1.93907 Influence of hot carriers on the temperature dependence of threshold in 1.3μm InGaAsP lasers Appl. Phys. Lett. 41, 1018 (1982); 10.1063/1.93395

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Spatially resolved observation of carrier leakage in 1.3-l-lm In1_xGaxAsyP1_y lasers

Liang-Hui Chen,a) J. C. V. Mattos, F. C. Prince, and N. B. Patel Institutode Ffscia "Gleb Wataghin. "Universidade Estadual de Campinas. UN/CAMP. 13100 Campinas. SP. Brasil

(Received 19 October 1983; accepted for publication 12 December 1983)

We report spatially resolved observation of carrier leakage over heterobarriers between a thin InGaAsP active layer (eg-0.9 eV) and symmetric InGaAsP confining layers (Eg-1.28 eV), in a double-heterostructure laser. Peaks of short wavelength emission of about 1 f-lm were found to originate from the confining layers indicating that significant carrier leakage, not only of electrons but also of holes can occur. Additional experimental observations suggest that the surprising observation of significant hole leakage may be due to the existence of hot holes created by Auger and/or intervalence band absorption processes.

PACS numbers: 42.SS.Px, 73.40.Lq, n.20.Jv

InGaAsP double-heterostructure lasers operating at about 1.3 f-lm are near-ideal light sources for long distance optical communications systems because of several inherent advantages such as low loss and zero dispersion of fibers at this wavelength. One serious practical problem is the strong dependence of threshold current on operating temperature. For explaining this temperature dependence, several mecha­nisms have been suggested, amongst them, carrier leakage over the heterobarrier into the confining layer,1.2 interva­lence band absorption,3 and Auger recombination.4 How­ever, it is still an open question as to which mechanism domi­nates the temperature dependence.

In this letter we report experimental evidence of carrier leakage (both electrons and holes) over heterobarriers in 1.3-f-lm InGaAsP double-heterostructure lasers with quater­nary' confining layers studying the near band-gap shorter wavelength emission from confining layers with the help of a spatial scanning system. To our knowledge this is the first spatially resolved measurement for direct observation of car­rier leakage and the first direct evidence for hole leakage in InGaAsP lasers.

The lasers used for these measurements had 7-f-lm-wide

Go InA. P/lnP

diode u .. d I' n01 la,lnQ T -300·1(

CWoperallnQ

12000 13000

WAVELENGTH (.0.)

220mA

14000 9500

GolnAt P/lnP I diode ultd i, nollollnQ

T- 300 01(

2M rnA CWaperoUn;

10000 10500

wAlELENGTH tAl

FIG. I. Electroluminescence emission spectra of GaInAsP IInP diode with different injection currents. The emission near the second peak at ~ I.O-,um wavelength is shown amplified and separated from the main peak for rea­sons of clarity.

"On leave from the Semiconductor Institute. Chinese Academy of Sci­ences, Beijing, China.

oxide stripes and the doping of the various layers is the fol­lowing: n-InGaAsP confining layer (- 1.28 eV band gap) - 2 X 10 IH cm -3, undoped InGaAsP active layer with back­

ground doping _10 16 cm-\p-InGaAsP (-1.28 eV band gap) confining layer - Sx 10 17 cm- 3. Electroluminescence was measured by using a conventional lock-in system with a chopping frequency of about 100 Hz in cw operation mode, and using a Boxcar system in pulsed operation mode, with current pulses of width about 1.5 f-ls, and repetition of about 1 kHz. The radiation emitted from the diode was detected by a cooled InAs photovoltaic detector or a Ge diode for wave­lengths near 1.3 f-lm and by a cooled GaInAs photomulti­plier for wavelength near 1.0 f-lm.

Figure 1 shows the spectrally resolved emission of the laser diode taking injection level as parameter. Besides the 1.3-f-lm emission corresponding to the energy gap of active layer, there exists a short wavelength emission with peak at ~. 1.0 f-lm. The integrated intensities of the 1.0- and 1.3-f-lm emissions are plotted as functions of the injection current in Fig. 2 for another diode. It can be seen that the intensity of 1.0-f-lm emission is approximately proportional to the injec­tion level, but after lasing, the slope of curve is reduced ap­preciably. Also this intensity increases very quickly with in­creasing temperature.

8 [ -129·C -55·C -30·C o.c

7 ~-

GaInAs PI InP

-- I 3IJm ~misSlon! ------ I OlJm emlssloni

J 100 200

INJECTION CURRENT (rnA)

FIG. 2. Variation of integrated electroluminescence intensity injection as a function of current for the emission peaks at 1.3 and 1.0,um.

520 Appl. Phys. Lett. 44 (5), 1 March 1984 0003-6951/84/050520-03$01.00 © 1984 American Institute of Physics 520

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1.3 ~m ___ ~~ __ _

I.O~m

~ II"

T

N - quaternary

ConfininCjt la)'er

N- InP

Substrate

FIG. 3. Spatial distribution of the L3-l1m and LO-l1m emissions, at the cleaved face of the device. The relative intensities are not normalized.

To explain the origin of the short wavelength emission, several possibilities can be considered, such as (1) the recom­bination due to transition from conduction band to split off valence band,6 (2) p-n junction misplacing from heterostruc­ture interface to confining layer, or (3) carrier leakage from active layer to confining layers. In this situation, it is impor­tant to locate the emission region of short wavelength radi­ation and compare it with the position of 1.3-,um emission which should be located at the active layer. For this purpose, we measured the spatially resolved spectra of laser diode using a scanning system. The near field pattern oflaser diode after amplification is imaged at the entrance slit of a spec­trometer making the junction plane parallel to it. The image is scanned across the slit moving the common mount of the laser and the lens.

Figure 3 shows the spatial distribution of 1.0-,um radi­ation and the 1.3-,um radiation, the latter serving as a cali­bration mark to locate the position of the active region. It is clear that the 1.0-,um radiation originates from both sides of the active layer, that is, the regions emitting the 1.0-,um emis­sion are the confining layers. The emission energy corre­sponds to band to band recombination in the confining lay­ers (band gap -1.28 eV).

We can exclude the possibility of p-n junction misplac­ing from the heterojunction to the confining layer, because in

N-InP N-Q N-Q P-Q confining active confining

Substrate layer layer layer

~---J~ -------------;~-%-/ ~------.- -.--.-._. ¢:=J hot hole

FIG. 4. Energy-band diagram of L3-l1m InGaAsP/InP double-hetero­structure laser with quaternary confining layers. The split-off valence band is indicated by dot-dashed line. The arrows indicate a possible route for hot hole leakage.

521 Appl. Phys. Lett., Vol. 44, No.5, 1 March 1984

1 - 400 400 c - 300 300 >-r- ::i ;;; 200 z w •

200 ~ r-

r-":' • z

w 0: 0:

z 100 0 100 :> u

v; '"

" 70

w

0

70 -' 0 I

'" E ~

50 w a:: I

0 r-

30

~ 30

20 20

10 1 10 130 200 250 300 350

TEMPERATURE (OK)

FIG. 5. Variation of LO-l1m emission intensity at a fixed current and of threshold current density as a function of operating temperature.

that situation we should find a single peak in the n-confining layer. Besides we measured the V-I characteristic of the laser diode, finding that the knee point of the forward voltage is about 0.9 V corresponding to the active layer. Also the 1.0-,urn emission has a strong temperature dependence, increas­ing with temperature near room temperature and practically nonexistent below - 250 K. It can be concluded that the origin of the short wavelength emission is carrier leakage from the active layer to the confining layers. Figure 3 shows that hole leakage is at least as important as electron leakage. This result is surprising since from calculations7

•H hole leak­

age is expected to be negligible. We speculate that the hole leakage observed by us may be in large part caused by the existence of hot holes in the split-off band in the active lay­er6

•9 as shown in Fig. 4. These hot holes may be a conse­

quence of either an Auger process or of intervalence-band absorption. The partial saturation of the I .O-,um emission at lasing threshold seen in Fig. 2 indicates that the Auger pro­cess may be dominant.

Finally in Fig. 5 we see that the temperature depen­dence of the total I.O-,um intensity P can be expressed as P a:: exp( T IT OL ), where T OL is a characteristic temperature of this process. The value of T OL ~80 ·C is comparable with the threshold current T 0 ~ 7 5 ·C of the same device.

One of the authors, Liang-Hui Chen, is greatly indebted to Professor Jose E. Ripper for his kind invitation to work in Brasil, to Professor Carlos A. Ribeiro for his forceful sup­port and valuable help, and to Professor N. Winogradofffor his concern and useful discussion. The authors would like to express their thanks to Mr. Antonio Jorge F. Mendes and to Mr. Emilio C. Bortolucci also for their effective assistance. This work is supported by F APESP and TELEBRAS.

'w. Ng and Y. Z. Lin, Electron. Lett. 16,69411980). 2M. Yano, H. Imai, and M. Takasagawa, 1. Appl. Phys. 52, 3172 11981).

Chen etal. 521

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128.114.34.22 On: Tue, 02 Dec 2014 06:13:24

IA. R. Adams, M. Asada, Y. Suematsu. and S. Arai. Jpn. J. App\. Phys. 19. L621 (1980).

"V. Homikoshi and Y. Fukukawa, Jpn. J. App\. Phys. 18,809 (19791. 'F. C. Prince, N. B. Patel, Shih-Lin Chang. and D. J. Bull, IEEE J. Quan­tum Electron. QE-17, 597 (1981).

"A. Mozer, K. M. Romanek, W. Schmid, and M. H. Pilkhun, App\. Phys. Lett. 41, 964 (19821.

'H. C. Casey, Jr. and M. B. Panish.lldaosrruc/llre La.len IAcadenlic. I\C\\ York. 197R1.

"T. R. Chen. U. Koren, S. Margalit, K. L. Yu. L. C Chill. A. H"S\on, and A. Yariv, App\. Phys. Lett. 42,1000 (19831

"Masamichi Yananishi. Ikuo Sllcmune. Kazahiro Nonomllra, and NohllO Mikoshiha, Jnp. J. App\. Phys. 21. L24(11982).

Polarization hysteresis in dielectric films using light diffraction by acoustic waves

Alfred E. Attard and John F. Kuehls Department of Defense, Ft. George G. Meade, Maryland 20755

(Received 20 September 1983; accepted for publication 13 December 1983)

A new method for determining polarization hysteresis in dielectric films is described. The technique is capable of determining the type of polarization as well as the relaxation time. Results are described for Mylar.

PACS numbers: 77.55. + f, 43.35.Sx, 77.30. + d, 78.20.Jq

The phenomenon of diffraction of light by traveling waves on a thin film has been described and analyzed pre­viously. 1,2 In this letter we describe how this effect provides a new technique to study the polarization hysteresis in thin films.

The experimental arrangement is similar to that pre­viously described 1,2 with changes as indicated in Fig. 1. The rf signal from the amplifier is coupled to the film electrode via a capacitor C which removes the dc component. A sepa­rate dc power supply is connected to the same electrode via inductance L. This arrangement permits independent vari­ation of the rf voltage Vrf and the dc voltage Vdc that are applied to the film electrode without changing the transfer characteristics of the amplifier. The film used in these ex­periments was Mylar (polyethylene terephthalate).

We will show that the intensity of the diffracted light provides a new method of measuring the polarization of the dielectric film via the electrostatic body forces. In particular, the variation of the intensity of the diffracted light with po­larization voltage or time provides a measure of the variation of the induced polarization of the Mylar film. In addition, the sequence of events in the diffracted intensity measure­ments determines the type of induced polarization. In the hysteresis measurements described here, the sequential uni­polar and bipolar data indicate that the induced charge must be homopolar.

Using this experimental arrangement, the intensity of the diffracted light was measured as a function of Vdc' The magnitude of Vrf was kept constant. The frequency content of the Vrf was monitored with a spectrum analyzer to ensure spectral purity. The incident light intensity was monitored to assure constancy.

(1) Unipolar hysteresis. In Fig. 2, the intensity of the diffracted light is displayed as a function of Vdc where the voltage is changed in magnitude only, and where the film has been previously polarized by an electric field of the same

polarity. Note the following features: (a) at zero dc voltage, diffraction is observed; (b) as the voltage increases, the inten­sity decreases until the intensity vanishes; (c) as the dc vol­tage increases further, the intensity increases again; (d) when the dc voltage is now decreased, the phenomenon is repeated with some slight shift; (e) the phenomenon is repeatable.

(2) Bipolar hysteresis. In Fig. 3, the intensity of the dif­fracted light is displayed as a function of the dc voltage which is now cycled over positive and negative values, and after several cycles have been established. Note the following features: (a) the arrows indicate the sequence of events; (b) beginning at zero dc voltage, the intensity of the diffracted light is not zero; (c) as the dc voltage increases, the diffracted light intensity increases; (d) when the dc voltage is then re­duced, the light intensity decreases to zero and then in­creases back to the initial value at zero dc voltage; (e) when the variations in dc voltage are repeated for the opposite polarity, the diffracted light intensity shows the same vari­ation; (f) at points C and D in the figure, the first order dif­fraction vanishes without the second order diffraction ap­pearing; (g) the effect is repeatable;

(3) Relaxation times. The intensity of the diffracted light at point A in Fig. 3 was determined as a function of time. We assume a relation of the form

I = In exp( - tiT).

c ~ f---r-----:.. ~ ~~==============W=AV~E~M~OT~'O=N~

MVLAR

L

COUNTER ELECTRODE

FIG. I. Detail of the transducer arrangement.

11)

522 Appl. Phys. Lett. 44 (5), 1 March 1984 0003-6951/84/050522-03$01.00 @) 1984 American Institute of Physics 522

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