Highpower buried InGaAsP/GaAs (λ=0.8 μm) laser diodesD. Z. Garbuzov, N. Ju. Antonishkis, S. N. Zhigulin, N. D. Il’inskaya, A. V. Kochergin, D. A. Lifshitz, E. U.Rafailov, and M. V. Fuksman Citation: Applied Physics Letters 62, 1062 (1993); doi: 10.1063/1.108795 View online: http://dx.doi.org/10.1063/1.108795 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/62/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Effects of broad-waveguide structure in 0.8 μm high-power InGaAsP/InGaP/AlGaAs lasers Appl. Phys. Lett. 75, 1839 (1999); 10.1063/1.124845 Modulation bandwidth of highpower single quantum well buried heterostructure InGaAsP/InP (λ=1.3 μm)and InGaAsP/GaAs (λ=0.8 μm) laser diodes Appl. Phys. Lett. 68, 1186 (1996); 10.1063/1.115963 Temperature dependence of threshold current density J th and differential efficiency η d of highpowerInGaAsP/GaAs (λ=0.8 μm) lasers Appl. Phys. Lett. 66, 253 (1995); 10.1063/1.114193 Theoretical investigation of minority carrier leakages of highpower 0.8 μm InGaAsP/InGaP/GaAs laserdiodes Appl. Phys. Lett. 65, 2260 (1994); 10.1063/1.112738 Highpower InGaAsP/GaAs 0.8μm laser diodes and peculiarities of operational characteristics Appl. Phys. Lett. 65, 1004 (1994); 10.1063/1.112206

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High-power buried InGaAsWGaAs (il=O.8 pm) laser diodes D. Z. Garbuzov, N. Ju. Antonishkis, S. N. Zhigulin, N. D. Il’inskaya, A. V. Kochergin, D. A. Lifshitz, E. U. Rafailov, and M. V. Fuksman A. I? Ioffee Physico-Technical Institute, Russian Academy of Sciences, 26 Polytechnicheskaya st. I94021 St. Petersburg, Russia

(Received 27 July 1992; accepted for publication 11 December 1992)

Buried InGaAsP/GaAs (;1=0.78 km) separate confinement-single quantum well laser diodes have been prepared and studied for the first time. It has been shown that a stable far field pattern can be observed even at 500 mW continuous wave (cw) output power for diodes with active region width of about 7 pm, and single zero-mode operation has been obtained up to 170 mW cw for diodes with a width of 3.8 pm. Mirror facet overheating for the diodes studied was an order of magnitude less than that for similar AlGaAs/GaAs diodes.

Recent developments in separate confinement-single quantum well (SCH-SQW) structures brought about a dramatic increase in the maximum output power of AlGaAs/GaAs single-mode, single-element laser’.’ due to a reduced optical power density inside the active region.14 However, a local temperature increase of the mirror facets at high optical densities in these lasers remains significant and is certain to affect the maximum power and lifetime of the devices.5*6 In our earlier studies,4’6’7 devoted to investi- gations of broad area A-O.8 ,um, SCH-SQW laser diodes in the InGaAsP/GaAs system, we noted, among other ad- vantages of these Al-free diodes, a significantly lower mir- ror facet overheating as compared to analogous AlGaAs/ GaAs lasers.

In this letter we present first results of research on buried, index guided InGaAsP/GaAs laser diodes. Be- cause of the absence of easily oxidizing Al compounds it was possible to use in the processing of these lasers chem- ical etching of mesas with their subsequent regrowth with blocking layers, a technique widely used with InGaAsP/ InP system. An as-grown SCH-SQW InGaAsP/GaAs structure and a buried diode are shown schematically in

s SCH SQW I= 0.8 pm

I I N; P

---f undoped +

d (mm)

W=7um

FIG. 1. Band diagram and schematics of the laser diode.

Fig. 1. The four-layer Ino.49Ga0.51P p-n-p-n blocking struo ture was formed in a regrowth process. Care was taken to reduce current leakage at the mesa periphery.8 The results considered below have been obtained on laser diodes with cavity length of about 0.8 mm having their rear mirror facets coated with a highly reflective Si-SiO, coating.

The lasers were bonded with indium solder onto a cop- per heatsink p-side down. Figure 2(a) shows a continuous wave (cw) light-current characteristic and a low-current part of the light-current characteristic measured in a pulsed (r= 100 ns) mode for two diodes having a 7 pm wide active region. The far-field pattern in the junction plane was formed by contributions from zero and nonzero transverse modes (Fig. 3) and remained stable throughout the range of cw output power studied (up to 0.5 W). The maximum light output reached was about 0.5 W under cw operation and 1.2 W under pulsed operation.

The emission spectra of the diodes whose far-field pat- terns are similar to those shown in Fig. 2(b) were usually doublets with components separated by about 2 nm. As found from the spectra recorded at different viewing angles in the structure plane (Fig. 3), the long-wavelength com- ponent of the doublet relates to the central lobe of the far-field pattern, and the shortwave component is predom- inant in the side lobes, that is, a spectral shift occurs be- tween the emission lines related to the zero mode and one

0.2 0.4 0.6 0.8 I.0 I(A)

FIG. 2. (a) Low current part of pulse and cw light-current characteris- tics for diodes with w=7 pm. (b) Far-field patterns in the p-n junction plane for one of the diodes.

1062 Appl. Phys. Lett. 62 (lo), 6 March 1993 0003-6951/93/l 01062-03$06.00 @ 1993 American institute of Physics 1062 I 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:

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. T 8 j O h ( n m

n .z I

5 I I

4 2. 3 ‘2 : ;

FIG. 3. Las ing spect ra co r respond ing to dif ferent lobes in the case of far-f ield pat terns of the type s h o w n in Fig. 2(b) .

of the t ransverse modes . It m a y b e s u p p o s e d that this shift or ig inates f rom dif ferent loss mechan isms for these modes : for the nonze ro m o d e nonselect ive losses outs ide the act ive reg ion cou ld domina te whe reas for the fundamenta l m o d e select ive losses d u e to absorp t ion in w e a k e r - p u m p e d a reas o n the per iphery of the act ive reg ion ad jacent to the b lock- ing layers can b e dominant .

O n e m o r e feature of the w = 7 p m d iode character ist ics is demons t ra ted in Fig. 4 wh ich shows a var iat ion of the far-f ield pat tern at constant output p o w e r ( 1 0 0 m W ) with increas ing heat s ink temperature . A s s e e n in Fig. 4, a n increase of tempera tu re effectively reduces the nonze ro m o d e contr ibut ion, so that at 7 0 “C the emiss ion b e c o m e s s ing le m o d e . Exper iments in wh ich the threshold current densi ty was inc reased not by samp le hea t ing but by in- c reas ing the output losses s h o w a simi lar effect, war ran t ing a conc lus ion that the increase in the densi ty of excess car- r iers in the act ive reg ion is the m a i n cause of the effect. Est imates m a d e us ing pub l i shed da ta’ s h o w that the dif-

2 P = I O O m W

5 3 0 T C 7 0 “C 9 c- 3 ..z i i s

AII, -15 0 C l5 -15 0 + I5

Far f ie ld pat terns (@ ,I

FIG. 4. Tempera tu re d e p e n d e n c e of far-f ield pat tern at constant output power P = 1 0 0 m W . Thresho ld current densi t ies for these temperatures; 1 5 C-36 m A ; 3 0 ‘C-48 m A ; 7 0 “C-90 m A .

1 0 0 2 0 0 3 0 0 4 0 0 5 0 0

I ( m A )

FIG. 5. T h e s a m e as in Fig. 2, but for a d iode with w=3 .8 pm. In addi t ion severa l las ing spect ra a re shown.

fe rence be tween the effective va lues of the refract ive index ( A n e ff) of the act ive reg ion a n d Ino. G a o .51P b lock ing lay- ers d o e s not exceed 0.06, so that the effect of the increase in the threshold carr ier densi ty o n A n e ff apprec iab ly reduce its value. lo

S ing le -mode , s ing le- f requency opera t ion has b e e n ach ieved in laser d iodes with w = 3 .8 p m (Fig. 5). A s s e e n f rom the f igure, for these d iodes the nonze ro m o d e contr i - bu t ion is less than 1 0 % u p to the output of the 1 5 0 m W , the m a x i m u m output p o w e r be ing abou t 3 0 0 m W .

T h e low absorp t ion losses n e a r the mir ror facets is the m a i n condi t ion for h igh output p o w e r opera t ion of I n G a A s P / G a A s d iodes. P h o to luminescence techn ique was app l ied to detect the local tempera tu re r ise (AT) n e a r the mir ror facets.” T h e m e a s u r e d curves of A T versus dr iv ing c.urrent a n d output p o w e r for laser d iodes with w = 7 y m a re s h o w n in Fig. 6 (sol id curves). T h e ob ta ined va lues of A T represent a s u m of the contr ibut ions f rom the act ive

FIG. 6. So l id curve is the total m i r ro r facet overheat ing for d iode with w = 7 p m . D a s h e d curve represents a n ext rapolat ion for a bu lk act ive re- g ion tempera ture r ise ATs=Rr(IU-P,, , ) , whe re & - d i o d e thermal re- sistance, IU-electr ic power , P o P t-d iode opt ical output power .

1 0 6 3 App l . Phys. L&t., Vol . 62, No. 10, 8 M a r c h 1 9 9 3 G a r b u z o v et al. 1 0 6 3 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:

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region bulk (AT,) and the optical mirror facet overheat- ing (AT,,,). The dashed line is the extrapolated curve for AT, the value of the diode thermal resistance having been determined under the assumption that below the threshold current AT= AT,. As one can see from Fig. 6, the over- heating of the mirror facets due to optical absorption is less than 10 “C! even at P=O.37 W, which is an order of mag- nitude less than that in AlGaAs/GaAs lasers at the same level of the optical power density.5

Summing up the results, in the very first experiments with buried InGaAsP/GaAs lasers the output powers ob- tained are only slightly below the highest values known for AlGaAs/GaAs diodes of -a comparable aperture. ‘J The above results of measurements of the light-current charac- teristics (Figs. 2 and 5) and of the mirror local tempera- ture rise (Fig. 6) permit a conclusion that the excellent properties of the mirrors are capable of increasing the cw optical power of single-mode InGaAsP/GaAs lasers still more by factor 2-3. For this purpose one should (i) reduce the bulk active region overheating, and (ii) optimize the zero-mode lasing conditions. Our analysis shows that the buried lasers offer a real potential for the solution of both these problems, and it is along these lines that our efforts are going to be focused.

The authors express their thanks to N. I. Katsavets for participation in the measurements, Zh. I. Alferov for his interest in this work, and to Alexander von Humboldt- Stiftung for support of the final stage of the work.

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Published without author corrections

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