n-channelingaas quantum well lasingthyristor ...excellent electrical switching characteristics with...

Active and Passive Elec. Comp., 1998, Vol. I, pp. 73-78Reprints available directly from the publisherPhotocopying permitted by license only

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N-CHANNEL InGaAs QUANTUM WELLLASING THYRISTOR (QWLT) PREPARED

BY MOLECULAR BEAM EPITAXY

H.C. CHEN

Department ofElectrical Engineering, Far-East Junior College of Technologyand Commerce, Tainan, Taiwan 744, Republic ofChina

(Received 1 7 June, 1996)

N-channel lnGaAs quantum well lasing thyristors (QWLT) based on regenerative loop ofpotential barrier lowering resulted from the forward biased pn junction is demonstrated in aAIGaAs/GaAs double heterostructure. Excellent electrical switching characteristics with ahigh voltage control efficiency rlv (--Vs/VH) of 6.7 have been obtained when the device isoperated in the dark. Typical OFF- and ON-state resistances are 150K.Qand 10f respec-tively. A lasing threshold current density, front slope efficiency, and external differentialquantum efficiency measured in as-cleaved device are 183A/cm2, 0.4mW/mA, and 31%,respectively. The peak emission wavelength is centered at about 980nm.

1. INTRODUCTION

III-V semiconductor negative differential resistance (NDR) devices withelectrical- and optical- induced switching characteristics have found appli-cations in a variety of areas such as microwave generation and high-fre-quency oscillation. Of particular interest is the development of S-shapedNDRdevices,including metal-insulator-semiconductor1, pn junction2, anddelta-doped superlattice3 devices, in which they have high-speed features.However, most studies have concentrated on the in- vestigation of electri-cal properties.Recently, double heterostructure optoelectronic switches (DOES) have

been developed in GaAs/A1GaAs4, Si/SiGe5, and InP/InGaAsP6 materialstructures, which are all mainly based on an inversion charge sheet at theinternal heterojunction interface. The combination of both electrical andoptical switching properties has become a promising feature for optoelec-

73

74 H.C. CHEN

tronic integration.7 For a DOES constructed by a direct band-gap materialsystem, the impedance is high and there is no emission of light in theOFF-state. However, the impedance is low and strong emission of lightoccurs in ON-state. The switching phenomenon between two states couldbe induced by either electrical or optical triggering.

In this work, a new n-channel InGaAs single quantum well DOES, i.e.,QWLT prepared by molecular beam epitaxy (MBE) has been fabricated.The optical thyristor essentially combines the triangular barrier switch andsingle quantum well (QW) GaAsflnGaAs structure into a DOES. The useof the strained InGaAs layer offers the potential of a lower threshold cur-rent when lasing8, the lighter electron-hole mass, and higher mobility thanthose of GaAs QW structures. To our knowledge, the QWLT is the firstswitching device reported for a GaAs/InGaAs material system with a las-ing operation in the switching ON-state.

2. EXPERIMENTAL

The schematic cross section of the QWLT is depicted in Fig. 1. The struc-ture was grown by MBE on a (100)-oriented n/-GaAs substrate. Si and Bewere used as n- and p-type dopants, respectively. This structure con-tained a 0.51xm-thick (n+=2xl018cm-3) GaAs buffer layer, a 0.15txm- thick

delta-layer

0.2m p+-. GaAs 1E19 cm-30.15prn p+_ Al,,Gao,As 1518 cm-3Snm (()-AI Ga As 1519 cm"3

0.4 0.

ion i GaAs15nm i_lno,Ga As10nm GaAs

0:15/5’m p.-GaAs 1517 cm-30.15,rn N*- AIo.,Ga=8. As 2E18 cm"a0.5/Jm n+- GaAs 2E18 cm.3

n+-- GaAs SubstrateFIGURE Schematic cross section of the n-channel QWLT

QUANTUM WELL LASING THYRISTOR 75

(n/ 2 x 1018cm-3) Alo.4Gao.6As barrier layer, a 0.15gm-thick (px 1017cm-3) p-GaAs layer, a 15nm-thick undoped Ino.2Gao.8As QW

sandwiched with two 10nm-thick undoped GaAs layers, a 5nm-thick (n/

1 x 1019cm-3) Alo.4Gao.6As charge sheet layer, a 0.15gm-thick (p/x 1018cm-3) Alo.4Gao.6As barrier layer, and a 0.2gm-thick (p/x 1019cm3) GaAs cap layer. For fabricating a broad area laser, the

p/-side was metallized with Au/Zn and then the substrate was thinned to athickness of-- 100gm. Au/Ge was evaporated on the n-side and the waferwas then al- loyed. The area of the laser bar was 200gmx300gm aftercleaving. Electrical current-voltage (I-V) characteristics were measured bya Tektronix 370A curve tracer at room temperature.

3. RESULTS AND DISCUSSION

The A1GaAs/GaAs heterojunction potential barrier and InGaAs QW struc-ture with higher valence band offset are used to improve the localized con-finement of the holes. For a-n-channel DOES7, the basic principle of thesetriangular barrier-based thyristors is that NDR is caused by an increase ofelectron injection to the potential barrier maximum with an increase in theforward biased pn junction; then the triangular barrier rapidly collapses,leading to a fast switch from a high-impedance OFF-state to a low-imped-ance ON-state. The experimental I-V characteristic at room temperature isshown in Fig. 2. The measured switching parameters of the QWLT atroom temperature are switching voltage Vs=12.8V, switching currentIs=80gA, holding voltage VH=I.8V, respectively. With increasing appliedvoltage IH is 17mA, while with decreasing applied voltage, IH drops to4.4mA. This hysteresis is a result of electrical oscillations in the device,caused by the interaction of the NDR with parasitic circuit resistance.9 I-Vcharacteristics in the ON- state are all independent of external voltage dueto inherent properties of pn junctions. The resistance in the OFF-state istypically greater than 150Kf and the ON-state resistance is lower than10D, The observed switching and holding voltage lead to a high voltagecontrol efficiency, fly (= Vs/VH), of 6.7. This voltage control efficiency isamong the largest reported so far in a field represented by DOES.4"6

The optical characteristics of the as-cleaved lasing QWLT were measuredunder pulsed con- dition at room temperature. In the case of pulsed opera-

76 H.C. CHEN

tion, the pulse width was 501.ts with a repetition rate of 1KHz. Fig. 3 showsthe pulsed power output versus current and spectrum (inset) measured at abias current equal to the threshold current. The threshold current Ith wasmeasured to be 110mA, with a front slope efficiency of 0.4(mW/mA), andyielded 14mW, at a current of 134mA. The extemal differential quantumefficiency is as high as 31%. Although the Ith is large, it is the first experi-mental realization of a lasing device in n-channel A1GaAs/GaAs/InGaAs-based DOES. Hence, it is pointed out that while this device has not beenoptimized, better laser cavity ge- ometries are expected to allow thedecrease of Ith. In addition, the spectrum of the optical output is alsoshown in Fig.4, at a current I=l.lIth. As can be seen, the QWLT lases at anemission wavelength about 980nm with a spectrum full width at half max-imum (FWHM) of 2nm.

7"gP. 370A

VERT/D V

2mA

CURSOR

HORIZ/DIV

2V

CURSOR

PER STEP

5On^

OFFSET

O. On^

B 9m/DIV40K

X OF COLLECTORPEAK VOLTS

93.1

AUX SUPPLY0,00 V

FIGURE 2 Room temperature I-V characteristic of the QWLT

QUANTUM WELL LASING THYRISTOR 77

16

14

12

4

2

0

Pulse Width: 50 psec

Re=petition Rate: lOOOHz

0 50 O0 150Current (mA)

FIGURE 3 Pulsed power output versus current of the QWLT

Pulse Width: 50Repetition Rate:T=3OOK

,,t ,1, I...

991inn

FIGURE 4 Emission intensity versus wavelength of the QWLT measured at a bias currentI=1. llth

78 H.C. CHEN

4. CONCLUSIONS

We have successfully exploited for the first time an n-channel InGaAs QWinfrared laser diode operating at a wavelength of 980nm on switchingusing A1GaAs/GaAs/InGaAs double heterostructure. The lasing thresh-old current is 110mA, corresponding to a current density of 210A/cm2, andthe external differential quantum efficiency is 31% at room temperature.I-V switching characteristics are excellent and reproducible with a highvoltage control efficiency of 6.7. The inherent properties of electricalbi-stability and laser emission suggest the possibility of the QWLT for op-toelectronic applications.

References[1] T. Yamamoto and M. Morimoto:"l’hin-MIS-structure Si negative-resistance diode’,

AppL Phys. Lett., 20, 269 (1972)[2] C.E.C. Wood, L.F. Eastman, K. Board, K. Singer and R.J. Malik: "Regenerative switch-

ing devices using MBE-grown gallium arsenide’, Electron. Lett., 18, 676 (1982)[3] E.E Schubert, J.E. Cunningham, and W.T. Tsang: ’Perpendicular electronic transport in

doping superlattices’, Appl. Phys. Lett., 51, 817 (1987)[4] G.W. Taylor, J.G. Simmons, A.Y. Cho, and R.S. Mand: ’A new double heterostructure

opto-electronic switching device using molecular beam epitaxy’, J. Appl. Phys., 59,596 (1986)

[5] S.J. Kovacic, J.G. Simmons, K. Song, J.P. Noel, and D.C. Houghton:’Si/SiGe digitalopto-electronic switch’, IEEE Electron Device Lett., EDL-12, 439 (1991)

[6] S.J. Kovacic, B.J. Robinson, J.G. Simmons, and D.A. Thompson:’InP/InGaAsP dou-ble-heterostructure optoelectronic switch’, IEEE Electron. Dev. Lett., EDL-14, 54(1993)

[7] G.W. Taylor, R.S. Mand, A.Y. Cho and J.G. Simmons:"Experimental realization of ann- channel double heterostructure optoelectronic switch", Appl. Phys. Lett., 48, 1368(1986)

[8] S.W. Corzine, R.H. Yan, and L.A. Coldren: ’Theoretical gain in strained InGaAs/GaAsquan- tum wells including valence-band mixing effects’, Appl. Phys. Lett., 57, 2835(1990)

[9] S.J. Kovacic, J.J. Ojha, J.G. Simmons, P.E. Jessop, R.S. Mand and A.J.S. Thorpe,"Optical and electrical oscillations in double heterojunction negative differential resist-ance devices", IEEE Trans. Electron. Dev., ED-40, 1154 (1993).

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