Room-temperature continuous and pulsed lasing of vertical-cavity, single-quantum-well, surface-emitting microlasers is achieved at ~983nm. The active Ga[sub][0-8]In[sub][0-2]As single quantum well is 100 [angstroms] thick. These microlasers have the smallest gain medium volumes among lasers ever built. The entire laser structure is grown by molecular beam epitaxy and the microlasers are formed by chemically assisted ion-beam etching. The microlasers are 3-50-μm across. The minimum threshold currents are 1.1 mA (pulsed) and 1.5 mA (CW)

Florez, L. T.

Harbison, J. P.

Jewell, J. L.

Lee, Y. H.

McCall, S. L.

Scherer, A.

English

Caltech Authors - Main

for the detection function at data rates up to 900Mbit/s, as 
limited by the differential carrier lifetime, and with a fibre-to- 
fibre amplification of around 10dB. (For the simultaneously 
amplified signals, these bit error rates can be achieved at  
multi-Gbit/s rates; we experimentally demonstrated 2 Gbit/s.) 
The mode of operation of the amplifier device we report here 
significantly increases the utility of laser amplifiers in photonic 
transmission and switching systems. 
We gratefully acknowledge K. Bergvall for the AR coating, 
and L. Atternas for providing the external cavity laser. 
M. GUSTAVSSON 
A. DJUPSJOBACKA 
Ericsson Telecom AB 
S-126 25 Stockholm, Sweden 
L. THYLEN 
References 
18th August 1989 
1 THYLBN, L., GRANESTRAND, P., and DJUPSJOBACKA, A.: ‘Optical 
amplification in switching networks’. Proc. 1st OSA topical 
meeting on photonic switching, Incline Village, 1987, Paper PDP 8 
2 O’MAHONY. M. J.: ‘Semiconductor laser optical amplifiers for use in 
ruture fiber systems’, J .  Lightwave yechnol., 1988, LT-6, pp. 
531-544 
IKEDA, M., OHGUCHI, O., and YOSHINO, K.: ‘Monolithic LD optical 
matrix switches’. Proc. 13th Europ. conf. on optical communica- 
tion, 1987 
GUSTAVSSON, M., and THYLBN, L.: ‘Switch matrix with semicon- 
ductor laser amplifier gate switches: a performance analysis’. Proc. 
2nd OSA topical meeting on photonic switching, Salt Lake City, 
1989, pp. 18C182 
‘Integrated-optic device for high-speed databuses’, Electron. Lett., 
ALPING, A., BENTLAND, B., and ENG, s. T.: ‘100Mbit/s laser diode 
terminal with optical gain for fibre-optic local area networks’, ibid., 
GUSTAVSSON, M., KARLSSON, A., and THYLBN, L.: ‘A travelling wave 
semiconductor laser amplifier for simultaneous amplification and 
detection’. Proc. 10th OSA topical meeting on integrated and 
guided-wave optics, Houston, 1989, pp. 113-1 16 
GUSTAVSSON, M., THYLBN, L., DJUPSJOBACKA, A., and KARLSSON, A.: 
‘Travelling wave semiconductor laser amplifiers for simultaneous 
amplification and detection: systems experiments’. Proc. 2nd OSA 
topical meeting on photonic switching, Salt Lake City, 1989, pp. 
159-161 
THYLkN, L., DJUPSIOBACKA, A., JANSON, M., and dLDISSEN, W.: 
1985,21, pp. 491-493 
1984.20, pp. 794-795 
~~ 
9 GUSTAVSSON, M., KARLSSON, A., and THYLEN, L.: ‘Travelling wave 
semiconductor laser amplifier detectors’, submitted for publication 
10 OLSHANSKY, R., su, c. B., MANNING, J., and POWAZINIK, w.: ‘Mea- 
surement of radiative and nonradiative recombination rates in 
InGaAsP and AlGaAs light sources’, IEEE J .  Quantum Electron., 
1984, QE-20, pp. 838-854 
ROOM-TEM PERATUR E CONTINUOUS-WAVE 
VERTICAL-CAVITY SINGLE-QUANTUM-WELL 
M ICROLASER DIODES 
Indexing terms: Semiconductor lasers, Quantum optics, LEDs 
Room-temperature continuous and pulsed lasing of vertical- 
cavity, single-quantum-well, surface-emitting microlasers is 
achieved at -983nm. The active Ga,.,In,.,As single 
quantum well is lOOA thick. These microlasers have the 
smallest gain medium volumes among lasers ever built. The 
entire laser structure is grown by molecular beam epitaxy 
and the microlasers are formed by chemically assisted ion- 
beam etching. The microlasers are 3-50-pm across. The 
minimum threshold currents are 1.1 mA (pulsed) and 1.5 mA 
( C Y .  
Vertical-cavity, surface-emitting lasers’“ have many potential 
advantages over conventional edge-emitting lasers owing to 
their inherent two-dimensional nature and very short cavity 
lengths. The previous results of the optically pumped lasers5 
and electrically pumped microlasers6 implied very low thresh- 
~ 
ELECTRONICS LETTERS 28th September 1989 Vol. 25 No. 20 1377 
old current for a single-quantum-well (SQW) microlaser with 
proper current injection into an active gain medium. 
We made various sizes (3-100pm) of electrically driven ver- 
tical cavity microlasers with a 100A-thick GaInAs SQW gain 
medium. The basic structure is a vertical pin junction where 
electrical current is injected through the bottom and top 
mirrors. The sample is grown on an Si-doped n+ GaAs sub- 
strate by molecular beam epitaxy. The bottom (output) mirror 
has 23.5 pairs of AlAs/GaAs quarter-wave stack and is Si- 
doped 3 x 10’8cm-3. The calculated reflectivity for the 
bottom mirror is 99.87% at  980nm. The top mirror consists 
of 15 pairs of AlAs/GaAs quarter-wave stack Be-doped 
5 x 10’’ cm-3, phase matching superlattices of GaAs/AlAs, 
30A of delta-doped (Be, 1 x 10’3cm-2) GaAs for p-type 
ohmic contact, and a 15008, thick gold film. The calculated 
reflectivity for the top mirror is 99.96% at  980 nm. The spacer 
region consists of a SQW of l 0 0 A  Ga,.,In,.,As active gain 
region surrounded by a pair of graded Al,Ga,_,As (x = 0.2- 
0.5) and Al,.,Ga,.,As layers so that the combined optical 
thickness is a full wave. The resultant microresonator should 
have very high finesse (> 1OOO) to  balance the very small gain 
from 100 A-thick Ga,.,In,.,As; otherwise, the lasing would 
not be observed. Mesas of diameter 1, 1.5, 2, 3, 4 and 5pm 
(Fig. l), and 5, 10, 25, 50, 100 and 200pm square are defined 
by chemically assisted ion-beam etching. A - 1500A-thick Ni 
layer is patterned on top of the gold film for etch mask. The 
mesas are etched about 4-6pm deep through the gold film. 
Fig. 1 Very small portion of vertical cavity microlasers of diameter 
1-5 pm 
Fig. 2 shows a CW laser output characteristic for a 5 p m  
square microlaser with 1.5 mA threshold at room temperature. 
The laser light is linearly polarised above threshold. The 
983 nm output passes through the polished GaAs substrate 
with only small loss. Room-temperature continuous lasing is 
observed for 5, 10 and 25pm microresonators with 1.5, 3.0 
and 13.0mA thresholds with no heat sinking applied. Contin- 
uous lasing is observed with up to  1.5-2.0 times the threshold 
current. For  larger CW current, heating seems to red-shift the 
gain region out of the Fabry-Perot resonance and the micro- 
laser stops lasing. Reduction of the current will again produce 
f 
lasing at the same power levels as before. If the current is 
raised greatly above this point, however, the microlasers are 
permanently damaged. 
Using 90 ns pulses, the threshold currents are the same 
(1.1 mA) for the microlasers of diameter 3-5pm, and 1.1, 2.3, 
12 and 45 mA for the microlasers 5, 10, 25 and 50pm square. 
The measured single-facet differential quantum efficiency is 
about 8-10%. The threshold currents are marginally lower 
than in the previous three-quantum-well microlasers,6 not 
three times better. For the larger devices (> 5 pm), the thresh- 
old current density stays almost constant at 1.8 kA/cm’. This 
value is still much larger than the theoretical’ minimum 
threshold current density (60 A/cmZ). For the smaller devices 
(< 5 pm), the threshold current density increases with the 
reduction in size, which we believe is due mainly to surface 
recombination of carriers. 
L O  I 1 
975 )f ? I 20 1 990 “m 
f 
0 1 2 3 
pig input , mA 
Fig. 2 Output against current for  5pm-square microlaser operating CW 
at room temperature without heat-sinking 
Inset shows spectrum at 1.8 mA. Spectral line width is 3.5 A, the 
resolution limit of spectrometer 
Since the maximum possible gain per pass from a SQW is 
of the order of any small loss of this magnitude can be 
critical for the lasing action. Possible sources for the loss are 
band-tail and/or free carrier absorption by highly doped 
impurities, a slight mismatch between the gain maximum and 
the peak reflectivity of the mirrors, and scattering. The electri- 
cal resistance through the heterostructure mirrors is rather 
high (between 565000 R depending on the sizes). This high 
resistance and high current density are the main problems 
preventing continuous operation at high driving currents. 
Reduction of the resistance and better heat sinking should 
make more efficient room-temperature continuous micro- 
lasers. 
In summary, we have demonstrated single-quantum-well 
(100 &thick GaInAs), surfaceemitting microlasers with 
minimum thresholds of 1.1 mA (pulsed) and 1.5 mA (CW) at 
room temperature. These microlasers have the smallest gain 
medium volumes of any lasers ever built. Even though the 
microlasers are not optimised in the present form, the thresh- 
old current is low enough to consider driving arrays of micro- 
lasers simultaneously. We can expect another order-of- 
magnitude reduction in the threshold current (less than 
100pA with a 2-3V source) with proper improvement of 
design and processes involved. Arrays of very low threshold 
microlasers will be critical components for optical computing, 
chip-to-chip communication, and photonic switching. 
Y. H. LEE 
J. L. JEWELL 
A. SCHERER* 
S. L. McCALLt 
J. P. HARBISON* 
L. T. FLOREZ* 
A T L T  Bell Laboratories 
Holmdel, NJ 07733, USA 
21st July 1989 
*Bellcore 
Red Bank, NJ 07701, USA 
t AT&T Bell Laboratories 
Murray Hill, NJ 07974, USA 
References 
1 SAKAGUCHI, T., KOYAMA, F., and IGA, K . :  ‘Vertical cavity surface- 
emitting laser with an AlGaAs/AIAs Bragg reflector’, Electron. 
Lett., 1988,24, pp. 928-929 
2 IBARAKI, A., KAWASHIMA, K., NRUSAWA,  K., ISHIKAWA, T., YAMA- 
GUCHI, T., and NIINA, T. : ‘Buried heterostructure GaAs/GaAIAs 
distributed Bragg reflector surface emitting laser with very low 
threshold (5.2 mA) under room temperature CW conditions’, Jpn. 
BOTEZ, D., ZINKIEWICZ, L. M., ROW, T. I., MAWST, L. L., and PETER- 
SON, G.:  ‘Low-threshold-current-density vertical-cavity surface 
emitting AlGaAs/GaAs diode lasers’. Technical Digest of Con- 
ference on Laser and Electro-Optics, Paper FC2, Baltimore, 1989, 
p. 380 
4 FISHER, R.  J., TAI, K., HUANG, K. F., DEPPE, D., and CHO, A. Y.: 
‘Extremely low current threshold in vertical cavity surface emitting 
laser diodes by use of hybrid reflectors’, to appear in Appl. Phys. 
Lett. 
s. L., and CHO, A. Y.: ‘Vertical cavity single quantum well laser’. 
Technical digest, CLEO ’89 (Optical Society of America, Balti- 
more, Maryland), Paper PD 14-1; also to appear in Appl. Phys. 
Lett., 31st July 1989 
6 JEWELL, J. L., ~CHERER, A., MCCALL, s. L., LEE, Y. H., WALKER, s., 
HARBISON, J. P., and F ~ R E Z ,  L. T.: ‘Low-threshold electrically 
pumped vertical-cavity surface-emitting microlasers’, Electron. 
Lett., 1989, 25, pp. 1123-1 124 
7 YARIV, A.: ‘Scaling laws and minimum threshold currents for 
J .  Appl. Phys., 1989,28, pp. L667-L668 
3 
5 JEWELL, J.  L., HUANG, K. F., TAI, K., LEE, Y. H., FISCHER, R. I., MCCALL, 
quantum-confined -semiconductor laser’, Appl. Phys. Lett., 1988, 
53, pp. 1033-1035 
FABRICATION AND GAIN MEASUREMENTS 
FOR BURIED FACET OPTICAL AMPLIFIER 
Indexing terms: Optoelectronics, Integrated optics, Optical 
communications 
The paper reports the fabrication and gain measurements of 
buried facet optical amplifiers. Chip gain of 25 dB, gain ripple 
of < l d B  and gain difference of < l d B  for TE and TM- 
polarised light are observed. The gain is found to decrease 
rapidly with increasing temperature. This behaviour is 
explained using a model calculation of the radiative and non- 
radiative recombination rates in the active region of the 
amplifier. 
Optical amplifiers are currently of interest for applications in 
optical communication systems.’.’ Two important criteria for 
the performance of the optical amplifiers are (i) absence of any 
gain ripple, i.e. the modulation of the optical gain at residual 
cavity mode wavelengths be negligible, and (ii) the optical gain 
must be independent of the polarisation of the input light. 
This letter reports the fabrication and optical gain measure- 
ments of buried facet  amplifier^^,^ which exhibit very low gain 
ripple ( < l d B )  and IOW polarisation dependence of gain 
(< 1 dB). 
The buried facet configuration (Fig. 1) is useful for two 
reasons, (a) it provides a polarisation-independent reduction 
in reflectivity (by a factor of 56100) over a cleaved facet, and 
(b) it allows one to achieve effective reflectivities of or 
less reproducibly simply by putting a conventional anti- 
reflection coating ( -  lo-’) on the facet.4 
The fabrication of the device involves the following steps. 
The epitaxial layers consisting of the n-InP buffer layer, 
undoped GaInAsP (1 - 1.55 pm) active layer, p-GaInAsP 
(2 - 1.3pm) antimeltback layer, p-InP cladding layer and 
p-GaInAsP (2. - 1.3 pm) contact layer are grown on a (100)- 
oriented n-InP substrate by the liquid-phase epitaxy growth 
technique. Mesas are then etched on the wafer along (110) 
electrode ~ , 510, p - GaInAsP 
ant I melt back 
a b m  
Fig. 1 Schematic diagram of buriedfacet amplifer structure 
1378 ELECTRONICS LETTERS 28th September 1989 Vol. 25  NO. 20  


Room-Temperature Continuous-Wave Vertical-Cavity Single-Quantum-Well Microlaser Diodes

Low-threshold electrically pumped vertical-cavity surface-emitting microlasers’,

Low-threshold-current-density vertical-cavity surface emitting AlGaAs/GaAs diode lasers’.

Vertical cavity surfaceemitting laser with an AlGaAs/AIAs Bragg reflector’,

http://authors.library.caltech.edu/452/1/LEEel89.pdf

Room-Temperature Continuous-Wave Vertical-Cavity Single-Quantum-Well Microlaser Diodes

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