b.. '.. STUDY OF CYCLOTRON RESONANCE AND MAGNETO-PHOTOLUMINESCENCE OF N-TYPE MODULATION DOPED InGaAs QUANTUM WELL LAYERS AND THEIR CHARACTERIZATIONS N. KOTERA Kyushu Institute of Technology, Iizuka, Fukuoka 82U, Japan E. D. JONES Sandia National Laboratories, Albuquerque, New Mexico 87185, U. S. A. K. TANAKA Kyushu Institute of Technology, lizuka, Fuhoka 82, Japan H. ARIMOTO, M. OHNO, N. M I U M,, Institute of Solid-state Physics, University of Tokyo, Roppongi, Tokyo 16, Japan T. MISHIMA, Y. SHIMAMOTO, M. KOMORI, K. HIGUCHI Central Research Laboratory, Hitachi Ltd., Kokubunnji, Tokyo 185, Japan Two-dimensional natures of energy-band and the effective mass of conduction subband in narrow InGaAs/InAlAs quantum well layers have been clarified via magneto-photoluminescence, cyclotron resonance, Shubnikov-de Haas oscillations and quantum Hall effect, interband optical transmittance, and photoluminescence. Heavy effective masses of.7mo were determined in 5- and 1-nm-wide quantum wells, which were 7% larger than the bulk bandedge mass,.1mo. Sheet carrier concentration in the quantum wells was as high as 1 x 1l2 cm-2. 1 Introduction Nanoscale InGaAs/InAlAs multi-quantum well (MQW) structures are very important because they are widely used for photodetectors and light emitters. Bandgap energies of InGaAs quantum wells (QWs) were quantitatively treated using photoluminescence and magneto-absorption I. Electron effective mass for the motion parallel with a QW plane (in-plane mass) was reported to be..5mo where the carrier concentration was.2 x 1" cm-2. The mo denotes the electron mass in vacuum. So far, two-dimensional (2D) bandedge mass in a square well with high carrier concentration has not been evaluated. In this report, 2D characteristics of n-type InGaAs/InAlAs QWs were characterized by electrical transport and interband optical transmission and photoluminescence. Sheet electron concentration waq 1 x 1OI2 cm-2 and 2D electron gas in QWs was evidenced. At 2 I<, the effective mass in 5-nm-wide 1 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the Sandin is a mukipragram Iaboratony operated by Sandia Cotparation, a Lockheed Martin Company, for the United sates Department of Energy under contract DE-AC-9AL85m.
QWs was determined by infraxed cyclotron resonance. At 2 I<, magnetophotoluminescence of a single 1-nm-wide QW was measured and estimated mass was almost the same with the cyclotron mass. 2 Specimen Preparation The Ino.53Gao.7As/Ino.52Ab.8AsMQW layer was fabricated by MBE on InP crystals. The wafer specimen (named M5) had a 1-nm-thickundoped InAlAs cap layer on top, one modulation-doped InGaAs/InAlAs single QW layer of 1-nm-wide well, ninty-nine modulation-doped InGaAs/InA.lAs MQW layers of 5-nm-wide well, a 25-nm-thick undoped InAlAs buffer layer, and the semiinsulating InP substrate. The ninty-nine-multi QWs were composed of 5-nmwide InGaAs wells and 1-nm-wide InAlAs barriers. Si was homogeneously doped in the whole barrier region. Using double-crystal X ray deffraction, period of MQW layers was found 15.5 nm and agreed well with the process control target, 15 nm. 1 Energy (ev) 1.2 I Magnetic Field B (T) Fig.1 Absorbance (dotted line) and photoluminescence (solid line) spectra at 77 K. 3 Fig.2 Hall voltage (left lower trace) and sample voltage (left upper trace) vs magnetic field at 1.5 K. Optical and Electrical Characterizations Transmittance ( T )spectra normalized with incident light intensity were measured at 77 K. Absorbance was defined as (1- T ) and plotted by dotted lines in Fig. 1. The staircase-like spectrum including two steps was the evidence 2
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of interband allowed transitions. Photoluminescence (PL) excited by a He-Ne laser was measured and plotted in Fig. 1. PL peak energy agreed with the 2D fundamental absorption edge. M5 chip was selectively etched before PL measurements 3. For transport experiments, the chip was patterned and mesa-etched to get a Rail bar. At 1.5 K and a constant current of 1 PA, Hall voltage, V H and, sample voltage, Vx,were measured as a fucntion of magnetic field, B, as shown in Fig. 2. The VX curve showed clear Shubnikov-de Haas oscillations. The deepest minimum at 6.78 T corresponded to the third Landau level including both spins, where the Hall resistance for 99 layers was 3 R. From the oscillation period, sheet electron concentration was determined to be.98 x 1OI2 cm-2. For low-temperature experiments, the chip was patterned and mesaetched to get a Hall bar. At 1.5 K and a constant current of 1 PA, Hall voltage, VH,and sample voltage, VX,were measured as a fucntion of magnetic field, B, as shown in Fig. 2. The VX curve showed clear Shubnikov-de Haas oscillations. The deepest minimum at 6.78 T corresponded to the third Landau level including both spins, where the HaIl resistance for 99 Iayers was 3 R. From the oscillation period, sheet electron concentration was determined to be.98 x 1OI2 cm-2., 5 v).- f.5.l 5 11 Magnetic field B (T) Fig.3 Transmission vs magnetic field a$ 2 K. The lower trace is shifted downward by.5 for clarity. Cyclotron Resonance in Pulsed Magnetic Fields A single-turn coil technique was used to generate very high pulsed magnetic fields. A COz laser was used as a radiation source. Because of over-absorption phenomena in cyclotron resonance, the 99 MQW layers were etched to a half. The transmission signal normalized by zero-field transmission intensity, T(B)/T(O),was plotted as a function of field, B, as shown in Fig, 3. Clear resonance minima were observed for both wavelengths of 1.61 and 9,52 pm at 67 and 7 T. The ratio of Landau level energy to the field was 1.75 mev/t. Both resonance fields gave the same cyclotron effective mass of. 6 6 ~ From ~~. this effective mass, the zero-field Fermi level was calculated to be 36 mev which was close to the LO phonon energy, 33 mev or 29 mev, in InGaAs. 3
5 Magneto-Photoluminescence Magneto-photoluminescenceof 1-nm-wide single QW layer at the surface of M5 specimen was measured using Argon-ion laser. At 1.-2 K, four or less Landau transitions were observed as shown in Fig.. The peak energies of Landau transitions were proportional to the field, B, as shown in Fig. 5. Every straight line, fit on a series of peaks, passed through 82 mev at zero field which was the 2D bandgap at 2 K. I. 2.- h v C 2K 6 T 2 K h I. - a Y.8.9 ~ Energy (ev) Fig. Magneto-Photoluminescence spectrum measured at 2 K and 6 Tesla. 8 83?rn?Tw& Magnetic Field BQ Fig.5 Fan chart for 2 K magneto-photoluminescence peaks. To conclude, we have observed heavy- electron effective mass in InGaAs /InAlAs MQWs via magneto-photoluminescence and cyclotron resonance. The two-dimansional nature of the bands were confirmed by Shubnikov-de Haas oscillation, quantum Hall effect, transmittance, and magneto-photoluminescence. 1. 2. 3.. W. Stolz et al, P h p. Rev. 3 36 31 (1987-11). P. Maurel et al, Sernicond. Sci. Technot.2,695(1987). K. Higuchi et al, Jpn. J. Appl, Phys. 36, to be published. E. D. Jones et al, Proceedings of SPIE's International S y m p o s i u m o n Optoelectronics '97:to be published.