出席國際學術會議心得報告 出席國際學術會議心得報告 出席國際學術會議心得報告
計畫編號 NSC 95－2221－E－002－355
計畫名稱 中紅外線化合物半導體材料與元件(2/2)
出國人員姓名
服務機關及職稱 國立台灣大學電子工程學研究所研究生吳承潤
會議時間地點 2007/5/14~2007/5/16 Bad Ischl, Austria
會議名稱 第八屆中紅外線光電材料與元件國際會議
發表論文題目 InAsSb/InAsPSb quantum wells grown by gas-source molecular beam epitaxy
一、參加會議經過
MIOMD 聚集世界各地中紅外波段材料與元件的專家學者一同交流研究心得與成果，該 會議每一年半舉行一次。第八屆會議由 Linz 大學主辦於奧地利一處溫泉聖地 Bad Ischl 舉行，
共有三十餘場口頭報告，以及一場論文壁報展示與會者來自十多個不同國家。討論議題包含 各式雷射、發光器、光偵測器、光纖及其他被動元件與材料等。
二、與會心得
該會議共分為三天進行。參與會議給予我們瞭解世界上其他學者對於此相關領域的研究 成果以及進度，並得到自我檢視的機會。藉由此次會議得以觸發平日思考的死角，並獲得各 式觀點想法，亦能多瞭解其他未接觸的相關元件材料，增廣視野拓展所知，對於將來的研究 方向與想法有很不錯的啟發。
InAsSb/InAsPSb quantum wells grown by gas-source molecular beam epitaxy
C. J. Wu, G. Tsai, D. L. Wang, and H. H. Lin∗
Graduate Institute of Electronics Engineering, Department of Electronic Engineering, National Taiwan University, Taipei 106, Taiwan
Strained InAsSb/InAsPSb quantum well (QW) is a promising active medium for 3-5 µm mid-infrared (MIR) light emitters. Previous reports have demonstrated lasers [1] and light-emitting diodes (LEDs) [2] based on InAsSb/InAsPSb QW structures grown by metal-organic chemical vapor deposition (MOCVD). These studies found that the MOCVD grown arsenic-rich InAsSb/InAsPSb QWs possesses type-IIa band alignment. In order to improve the wavefunction coupling, a complicated five-layer InAsPSb/InAsSb/InAsP/InAsSb/InAsPSb QW structure with W-shape conduction band profile was proposed and utilized in their light emitters [3]. In this paper, we report the growth and optical properties of MBE-grown InAsSb/InAsPSb QWs. Photoluminescence (PL) study shows that these QWs are type-I.
The QW is composed of a 100-Å-thick strained InAsxSb1-x well (0.87<x<0.92) and a 250-Å-thick InAs0.665P0.232Sb0.103 barrier. Samples with 5-period QW were grown on (100) oriented n-type InAs substrate at 420 ~ 470ºC by a VG-V80H gas-source MBE. Antimony beam was supplied by an EPI Sb cracking cell. P2 and As2 beams were from a gas K-cell with a cracking temperature of 1000 ºC. A general thermal effusion K-cell was used to provide group-III In flux. The As composition of the InAsSb well can be controlled by AsH3 flow rate.
High resolution double crystal XRD and PL were used to investigate the structural and optical qualities of the samples.
Fig. 1(a) shows a series of PL spectra measured at different temperatures ranging from 10 to 300K for an InAsSb/InAsPSb QW. The temperature dependent peak energy and a best-fitted Varshni curve are plotted in Fig. 1(b). The PL energy is lower than the curve by 8.5-meV at 10K. Since the value is larger than the calculated exciton binding energy, we attributed the PL to the recombination of the excitons localized in the tail states. The exciton is then decomposed into electron and hole in the extended states at ~100K as can be seen in Fig. 1(b). The 8.5-meV binding energy, in fact, is consistent with the exciton dissociation temperature. Since the transition energy of the QWs is between the energy gaps of InAsPSb and InAsSb [4], the band lineup is type-I. Effective mass approximation [4] was used to calculate the energy states in the QWs. The band discontinuities were used as fitting parameters, and the PL energy at 128K, where the effect of binding energy can be neglected, was compared to the calculated energy for electron to heavy hole ground state transition. The best results are shown in Fig. 2. With those data in Fig. 2, we obtain the conduction and heavy hole valence band offsets for strained InAsxSb1-x/InAs0.665P0.232Sb0.103 (0.87<x<0.92) QW system, ∆Ec=0.62⋅x−0.52 and ∆Ev=1.14−1.14⋅x.
[1] A. Joullie’ ,E. M. Skouri, M. Garcia, P. Grech, A. Wilk, P. Christol, and A. N. Baranov,Appl. Phys. Lett., 76, 2499(2000).
[2] A. Stein, A. Behres, K. Heime, A. Wilk, P. Christol, A. Joullie, A. Brozicek, E. Hulicius, T. Simecek, S.
Rushworth, L. Smith, and M. Ravetz, 11th International Conference on Indium Phosphide and Related Materials, 95 (1999).
[3] P.Christol, P.Bigenwald, A. Wilk, A.Joullie, O.Gilard, H.Carrere, F.Lozes-Dupuy, A.Behres, A.Stein, J.Kluth, K.Heime, and E.M.Skouri, IEE Proc.-Optoelectron., Vol.147, No.3, 181(2000)
[4] I.Vurgaftman and J.R.Meyer, J.Appl.Phys., Vol.89, No.11, 5815(2001)
∗email: [email protected]
Fig. 1: The InAs0.92Sb0.08/InAsPSb MQW PL spectra and its energy peak compare to the
Fig. 2: Heavy hole valence (black circle) and conduction (red triangle) band offset between As-rich InAsSb and InAs0.665P0.232Sb0.103
0.87 0.88 0.89 0.90 0.91 0.92 0.93 0.00
As Mole Fraction in InAsSb
∆Ev
∆Ec
出席國際學術會議心得報告 出席國際學術會議心得報告 出席國際學術會議心得報告 出席國際學術會議心得報告
計畫編號 NSC 95－2221－E－002－355
計畫名稱 中紅外線化合物半導體材料與元件(2/2)
出國人員姓名
服務機關及職稱 國立台灣大學電子工程學研究所研究生蔡濟印
會議時間地點 2007/5/14~2007/5/16 Bad Ischl, Austria
會議名稱 第八屆中紅外線光電材料與元件國際會議
發表論文題目 Photoluminescence study on InAsPSb grown by gas-source molecular beam epitaxy
Photoluminescence study on InAsPSb grown by gas-source molecular beam epitaxy
Gene Tsai, D. L. Wang, and Hao-Hsiung Lin*
Graduate Institute of Electronics Engineering and Department of Electrical Engineering National Taiwan University, Taipei, 10617, Taiwan, R.O.C.
Quaternary InAsPSb is a promising material for mid-infrared (MIR) optoelectronic devices which are drawing more and more attention recently [1]. The alloy can be deposited on either InAs or GaSb substrates with nearly matched lattice constant and with energy gaps covering the 2 – 3.5 μm MIR spectral range. Despite the immiscibility problem [2] in the material growth, InAsPSb has been successfully prepared by liquid phase epitaxy (LPE) [3], metal-organic chemical vapor deposition (MOCVD) [4], and gas-source molecular beam epitaxy (GSMBE) [5]. In this paper, we report a study on the optical properties of MBE grown InAsPSb alloys.
A series of InAsxPySb1-x-y samples with arsenic composition from 0 to 0.68 were grown on (100) n-type InAs substrates at 470ºC by a VG-V80H GSMBE system. Details of the growth procedure were reported elsewhere [5]. The 1-μm-thick samples were inspected by X-ray diffractometry (XRD) and electron probe microanalysis (EPMA) for their structural and compositional analysis. Photoluminescence (PL) spectra of the InAsPSb samples, excited by a 530 nm laser, were taken through a SPEX-500M monochromator by a standard lock-in technique. Results of the characterizations along with the growth parameters for these InAsPSb samples are summarized in Table I.
Interestingly, the peak energy of 18K PL fluctuates between 0.43~0.47 eV in the whole studied range. By comparing the peak energy with the energy gap calculated by interpolating the reported energy gap of the related binaries with the consideration of bowing parameters, we found that all the peak energies are lower than the predicted energy gaps. The energy difference E is given in Table I. For samples with As composition smaller than 0.37, the E is unusually large, indicating a strong compositional disorder in the samples. Note that 0.37 is the boundary of immiscibility region that is calculated by DLP model [6] for lattice-matched InAsPSb at 470ºC. Results from XRD analysis also support the point of compositional inhomogeneity. Temperature dependent PL spectra of these samples were also studied. We compared the peak energy with the energy gap predicted by Varshni equation and found that the PL peak energy of the samples outside the immiscibility region is close to the calculated energy gap at high temperature, indicating that the samples are with good compositional homogeneity and show near band edge transition at high temperature. As can be seen in figure 1, PL peaks of C1770 follow the Varshni curve above 100K. On the other hand, the PL peak energy of the samples within the immiscibility region is always below the Varshni curve even up to room temperature.
In conclusion, we have studied the photoluminescence of MBE grown InAsPSb. For samples with high arsenic composition, luminescence from near band edge recombination is observed at high temperature. Detailed analysis on temperature dependent PL will be discussed.
[1] J. Wagner, C. H. Mann, M. Rattunde, and G. Weimann, Appl. Phys. A, 78, pp. 505 (2004).
[2] G. B. Stringfellow, J. Appl. Phys., 54, pp. 404 (1983).
[3] H. Mani, E. Tournie, J. L. Lazzari, C. Alibert, A. Joullie, J. Cryst. Growth, 121, pp. 463 (1992).
[4] Takashi Fukui and Yoshiji Horikoshi, Jpn. J. Appl. Phys., 20, pp 587 (1981).
[5] Gene Tsai, De-Lun Wang, Chia-En Wu, Chen-Jun Wu, Yan-Ting Lin, and Hao-Hsiung Lin, J. Cryst.
Growth, (to be published)
[6] G. B. Stringfellow, J. Cryst. Growth, 27, pp. 21 (1974).
Sample No. AsH3 (torr) PH3 (torr) In/Sb (BEP)
Tg
(oC) As P Sb PL peak @ 18K (eV)
E (eV) C1898 50 0.040 0.675 0.285 0.497 0.269 C1899 100 0.092 0.625 0.283 0.495 0.235 C1900 200 0.223 0.517 0.260 0.466 0.179 C1767 300 0.361 0.411 0.228 0.433 0.143 C1768 500 0.560 0.284 0.155 0.450 0.069 C1770 700
990 2.03 470
0.681 0.220 0.099 0.476 0.035
Table I: Growth parameters, composition, 18K PL energy, and energy difference
E of quaternary InAsPSb alloys. E is the energy difference between PL transition energy and calculated energy gap at 18K.
Fig. 1: Temperature dependent PL peak energy plot of sample C1770. A calculated Varshni curve is also displayed. The experimental data coincide with the curve when T>100K, indicating that the PL is from near band edge transition.