tag:blogger.com,1999:blog-83515066661477099592024-03-12T23:18:36.660-07:00Engineer in Wine CountryMBE guy in wine countryhttp://www.blogger.com/profile/11729854844886575971noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-8351506666147709959.post-54620959035185410852009-04-29T22:21:00.000-07:002009-04-29T23:21:01.063-07:00Do you want to work in the wine country?<script type="text/javascript"><br />var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");<br />document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));<br /></script><br /><script type="text/javascript"><br />try {<br />var pageTracker = _gat._getTracker("UA-8617726-1");<br />pageTracker._trackPageview();<br />} catch(err) {}</script><br /><br /><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9oIBQOhaq5dzeKegZZm-eCYY0p_j04SIk44Wwo04mwd-X4DmvaEGuFJ1z-KuMHdk2ih7FJUC-RDnue8wZvfqca1DWP8taxZlpZ9ySAqllZskaI1qUdcY7MK6MjLxPsmxYz9Sc0nS6VDgy/s1600-h/P1000113_2.jpg"><img style="margin: 0px auto 10px; display: block; text-align: center; cursor: pointer; width: 320px; height: 180px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9oIBQOhaq5dzeKegZZm-eCYY0p_j04SIk44Wwo04mwd-X4DmvaEGuFJ1z-KuMHdk2ih7FJUC-RDnue8wZvfqca1DWP8taxZlpZ9ySAqllZskaI1qUdcY7MK6MjLxPsmxYz9Sc0nS6VDgy/s320/P1000113_2.jpg" alt="" id="BLOGGER_PHOTO_ID_5330355106098212434" border="0" /></a><br />Do you want to work in the beautiful Sonoma county? Do you want to make $10,000 a week for 6 months? Do you want to have a lot of fun while you work? Would you like a job the content of which includes wine-tasting, wine country touring, hanging on Facebook and uploading videos onto YouTube? Here is your big chance!!<br /><br />Murphy-Goode winery of Healdsburg has put out a request for a wine country lifestyle correspondent. One has to be an excellent communicator, imaginative and inquisive. One should also be able to use Web 2.0 tools (Facebook, YouTube, blog, twitter, etc.) effectively to showcase the wine country lifestyle and has great marketing and public relation capability. For more information please check out the link: <a href="http://www.areallygoodejob.com/">a really goode job</a>. Once you're hired, you make $10,000 a month, they will take care of your accommodation in a single family house, and they will pay for your travel to/from your hometown.<br /><br />The one who's interested has to make a video of less than 60 sec to promote him/herself. Engineer would love to apply for the job but unfortunately my boss and colleagues wouldn't allow it and plus, I already have a house in the beautiful wine country.MBE guy in wine countryhttp://www.blogger.com/profile/11729854844886575971noreply@blogger.com0tag:blogger.com,1999:blog-8351506666147709959.post-8462979565455014542009-04-28T22:59:00.000-07:002009-04-30T22:56:15.359-07:00Castello di Amorosa winery<a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-O6_HXbBCBhKyZ8lT204KeWGvrtduLHPl-5j0LnV6a_2cM7mVYZMOsIQ7rd_CLGXLB88w5SiVHZcU8nxIjSVS_Lowq9bajo15r9mkC12QigWavRnFfJtMG3PUD3X3JHf64H3uFC4YstXR/s1600-h/P1080226_2.jpg"><img style="margin: 0pt 10px 10px 0pt; float: left; cursor: pointer; width: 180px; height: 320px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-O6_HXbBCBhKyZ8lT204KeWGvrtduLHPl-5j0LnV6a_2cM7mVYZMOsIQ7rd_CLGXLB88w5SiVHZcU8nxIjSVS_Lowq9bajo15r9mkC12QigWavRnFfJtMG3PUD3X3JHf64H3uFC4YstXR/s320/P1080226_2.jpg" alt="" id="BLOGGER_PHOTO_ID_5329991118765782002" border="0" /></a><br /><br /><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhphvQUcB2_kSqnVrzs3DPy7zruJoSx1UzvzP1xAt3y9dFMtCOZ6jZ4YQGuPZe2RbLJj0PzaNgfq6uSvM_ms1lgk0dfgxjwhdmtx84j-jdVWwhSMbh7WnelWw8MYYP22IhnQgeHNpaVysUR/s1600-h/P1080225_2.jpg"><img style="margin: 0px auto 10px; display: block; text-align: center; cursor: pointer; width: 320px; height: 180px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhphvQUcB2_kSqnVrzs3DPy7zruJoSx1UzvzP1xAt3y9dFMtCOZ6jZ4YQGuPZe2RbLJj0PzaNgfq6uSvM_ms1lgk0dfgxjwhdmtx84j-jdVWwhSMbh7WnelWw8MYYP22IhnQgeHNpaVysUR/s320/P1080225_2.jpg" alt="" id="BLOGGER_PHOTO_ID_5329990670828038226" border="0" /></a><br />Since it's a blog about an engineer (me) living in the wine country, there has to be some articles about wine and winery. Today I'm going to share with you one of the latest attractions in the Napa Valley, <a href="http://www.castellodiamorosa.com/index.cfm?method=homepage.showpage">Castello di Amorosa</a>.<br /><br />It's a fairly short drive from Santa Rosa, just go north along Calistoga Road and go over a hill on a winding road. Within half hour you will see a blue sign with italic <span style="font-style: italic;">Castello di Amorosa</span>. The sign is not too obvious so I went over the first time. The castle is built on top of the hill so you won't be able to see it from the entrance.<br /><br />The castle was built by Dario Sutti, great grandson of California pioneer vintner Vittorio Sattui. During his travel in an old VW van around Europe after his graduation from UC Berkeley MBA school, he developed a strong fascination about medieval architecture. And after resurrecting his great grandfather's dormant wine business (<a href="http://www.vsattui.com/">V. Sattui Winery</a>), he purchased a 171 acre vineyard property in Calistoga in 1993 and began contructing Castello di Amorosa Winery in 1994. He built the 121,000 square foot, 12th century style, authentic Tuscan castle winery with reportedly authentic Tuscan bricks and 30 million USD!<br /><br />The tour of the castle costs $25 per person (with reserved wine tasting). Tasting only costs $15. Engineer didn't go for the tour because his wife and kids fell asleep when they arrived. But he did go wine tasting.<br /><br /><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjPPWrCm2zWPDW9upv_1JPmqp8XA0s2exfIkM90KYfHJei87cGQ-ZzF4ZDjZyPBNcJmjcxcZIdWut10WyykWQRcIIKQ7nXLfi4HbhbacBC8awFNoyAZ_GuuVEOhGRvxvwSmEfbA8dTUuIIe/s1600-h/P1080236_2.jpg"><img style="margin: 0pt 0pt 10px 10px; float: right; cursor: pointer; width: 180px; height: 320px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjPPWrCm2zWPDW9upv_1JPmqp8XA0s2exfIkM90KYfHJei87cGQ-ZzF4ZDjZyPBNcJmjcxcZIdWut10WyykWQRcIIKQ7nXLfi4HbhbacBC8awFNoyAZ_GuuVEOhGRvxvwSmEfbA8dTUuIIe/s320/P1080236_2.jpg" alt="" id="BLOGGER_PHOTO_ID_5330728153236289938" border="0" /></a>The wine produced by the Castello di Amorosa can only be purchased in the winery or online at <a href="www.castellodiamorosa.com">www.castellodiamorosa.com</a>. Frankly speaking, the whites (Gewurztraminer, pinot bianco, and dessert wines) of the winery are a little too sweet in my taste. For reds I tasted the 2004 Il Barone Reserve Cabernet Sauvignon and it was too harsh for me, but surprisingly I found the 2005 La Castellana Reserve "Super Tuscan" blend smooth, elegant, complex, and fruity. The hand sealed wax on the closure surely looks interesting! This Super Tuscan blends 74% of Cabernet Sauvignon, 14% Merlot, and 12% Sangiovese. It is an elegant, complex wine, with good depth, volume and balanced with very velvety tannins providing length and a smooth, lingering texture.<br /><br />Engineer's taste is more inclined to blended reds: Bordeaux or Super Tuscan. Maybe we are supposed to blend different grapes into a god given beverage!<br /><br /><span style="text-decoration: underline;"><br /><br /></span>MBE guy in wine countryhttp://www.blogger.com/profile/11729854844886575971noreply@blogger.com0tag:blogger.com,1999:blog-8351506666147709959.post-58336955144075725592009-04-28T22:49:00.000-07:002009-04-30T22:24:29.847-07:00MBE Native Oxide Desorption<script type="text/javascript"><br />var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");<br />document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));<br /></script><br /><script type="text/javascript"><br />try {<br />var pageTracker = _gat._getTracker("UA-8617726-1");<br />pageTracker._trackPageview();<br />} catch(err) {}</script><br /><br /><p class="MsoNormal" style="text-align: justify;">Native oxide desorption process depends on various conditions such as the following:</p> <p class="MsoNormal" style="margin-left: 21.25pt; text-align: justify; text-indent: -21.25pt;"><!--[if !supportLists]--><span style=""><span style="">1<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->Temperature monitor calibration: including pyrometer and desorption mass spectroscopy (DMS); one has to take the viewport deposition, reflectance from heated effusion cells, etc. into consideration when measuring temperature using pyrometer, while the calibration of DMS is not easy, either.</p> <p class="MsoNormal" style="margin-left: 21.25pt; text-align: justify; text-indent: -21.25pt;"><!--[if !supportLists]--><span style=""><span style="">2<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->The gas species used for overpressure: Basically, using the same group V species as the group V component of the substrate will results in lower desorption temperature [1-3]. </p> <p class="MsoNormal" style="margin-left: 49.6pt; text-align: justify; text-indent: -28.35pt;"><!--[if !supportLists]--><span style=""><span style="">2.1<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->For InP substrate, according to [1] under P<sub>2</sub> overpressure the oxide (thermal oxide) desorbs within 5 min at 490<sup>o</sup>C (actually at 473<span style="font-family:PMingLiU;">±</span>6<sup>o</sup>C the (2<span lang="ZH-TW" style="font-family:PMingLiU;">×</span>4) surface is observed and the oxygen is below detection limit for the XPS measurement) and a (2<span lang="ZH-TW" style="font-family:PMingLiU;">×</span>4) reconstruction is observed. This report suggests that under P<sub>2</sub> overpressure, the appearance of the (2<span lang="ZH-TW" style="font-family:PMingLiU;">×</span>4) reconstruction can be regarded as a sign for the complete desorption of the oxide. On the other hand, heating in a flux of As<sub>4</sub> molecules results in the formation of an InAs layer at the top of the oxide, which strongly reduces the oxide desorption rate. The complete removal of the oxygen requires at least 520<sup>o</sup>C and typically leaves a 1-nm-thick overlayer of InAs. In this case RHEED gives no indication whether the surface is oxide free. </p> <p class="MsoNormal" style="margin-left: 49.6pt; text-align: justify; text-indent: -28.35pt;"><!--[if !supportLists]--><span style=""><span style="">2.2<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->Authors in [2] suggest from In-P-O phase diagram that the UV-ozone oxide prepared on InP substrate should have a composition of InPO<sub>4</sub>. The (2<span lang="ZH-TW" style="font-family:PMingLiU;">×</span>4) reconstruction emerges at the temperature of 528<sup>o</sup>C under P<sub>2</sub> overpressure. They claim the removal of thin oxides from InP surface is probably not a matter of simple decomposition of the oxide but rather involves a reaction with the overpressure species or the substrate. The results suggest that the most probable reaction is with atomic phosphorus to form volatile phosphorus oxide, of which the most prevalent one would be P<sub>2</sub>O<sub>3</sub>, and atomic In as following formula:</p> <p class="MsoNormal" style="margin-left: 21.25pt; text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="margin-left: 21.25pt; text-align: justify;"><span style=""> </span>3InPO<sub>4</sub> + 5P <span style="font-family:PMingLiU;">→</span> 4P<sub>2</sub>O<sub>3</sub> + 3In</p> <p class="MsoNormal" style="margin-left: 48pt; text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="margin-left: 48pt; text-align: justify;">The phosphorus from the substrate is the dominant driving force for the reaction and the reaction is both temperature and time dependent. During the desorption process there is a coexistence of areas covered by oxide and of some oxide-free regions which gradually increase in size until the oxide is desorbed. The phosphorus overpressure prevents decomposition of the oxide-free, exposed InP substrate surface. The free In atom from the reaction will evaporate rather than staying on the InP substrate. However, to the extent that a P<sub>2</sub> overpressure does not entirely replace all the atomic P lost from the substrate, which is due to thermo-etching at overheated temperature, even desorption under a P<sub>2</sub> overpressure would not result in a perfect interface between substrate and subsequent epilayer, namely In-ball will form.</p> <p class="MsoNormal" style="margin-left: 49.6pt; text-align: justify; text-indent: -28.35pt;"><!--[if !supportLists]--><span style=""><span style="">2.3<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->In [3] As<sub>4</sub> and/or<sub> </sub>Sb<sub>4</sub> are used to protect the surface during InP desorption. The authors show that even if the deoxidation is feasible using one of the different beam pressures, the less critical temperature control leading to a good surface quality is obtained under (As<sub>4</sub>+Sb<sub>4</sub>) combined pressures. However, in my opinion, using different group V species when desorbing native oxides is not recommended and should be avoided.</p> <p class="MsoNormal" style="margin-left: 21.25pt; text-align: justify; text-indent: -21.25pt;"><!--[if !supportLists]--><span style=""><span style="">3<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->Substrate temperature ramp rate: Some studies use very slow ramp rate (1<sup>o</sup>C/min) [2] while some studies use fast ramp rate (~50<sup>o</sup>C/min) [3]. The ramp rate should be established by oneself according to each system.</p> <p class="MsoNormal" style="margin-left: 21.25pt; text-align: justify; text-indent: -21.25pt;"><!--[if !supportLists]--><span style=""><span style="">4<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->The composition and the thickness of the native oxide: Thermal oxide will have a lower desorption temperature than ozone plasma oxide [4], the thermal oxide grown on GaAs substrate has a desorption temperature of 582<sup>o</sup>C (in this report the temperatures were measured using a Pt/Pt13%Rh thermocouple and the thermocouple was calibrated at the melting point of aluminum: 660<sup>o</sup>C). Whereas ozone oxide has a desorption temperature of 638<sup>o</sup>C. The authors attribute the 56<sup>o</sup>C difference to the composition difference of the two oxides. And desorption temperature can be used as an accurate thermal reference point in the MBE growth of GaAs. As for thickness, the thinner, the better, in order to reduce the desorption time [2].</p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;"><o:p> </o:p></p> <p class="MsoNormal" style="text-align: justify;">Reference</p> <p class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;"><!--[if !supportLists]--><span style=""><span style="">[1]<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->R. Averbeck <i style="">et al.</i>, “Oxide desorption from InP under stabilizing pressures of P<sub>2</sub> and As<sub>4</sub>,” <i style="">Appl. Phys. Lett., </i>vol. 59, pp. 1732-1734, 1991.</p> <p class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;"><!--[if !supportLists]--><span style=""><span style="">[2]<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->P. G. Hofstra <i style="">et al., </i>“Desorption of ultraviolet-ozone oxides from InP under phosphorus and arsenic overpressures,” <i style="">J. Appl. Phys.</i>, vol 77, pp. 5167-5172, 1995.</p> <p class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;"><!--[if !supportLists]--><span style=""><span style="">[3]<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->A. Godefroy <i style="">et al., </i>“X-ray and UV photoelectron spectroscopy of oxide desorption from InP under As<sub>4</sub> and/or Sb<sub>4</sub> overpressures: exchange reaction As<span style="font-family:Wingdings;"><span style="">ó</span></span>Sb on InP surfaces, “ <i style="">J. Crystal Growth, </i>vol. 179, pp. 349-355, 1997.</p> <p class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;"><!--[if !supportLists]--><span style=""><span style="">[4]<span style=";font-family:";font-size:7;" > </span></span></span><!--[endif]-->A. J. SpringThorpe <i style="">et al., </i>“Measurement of GaAs surface oxide desorption temperatures,” <i style="">Appl. Phys. Lett., </i>vol. 50, pp. 77-79, 1987.</p>MBE guy in wine countryhttp://www.blogger.com/profile/11729854844886575971noreply@blogger.com0tag:blogger.com,1999:blog-8351506666147709959.post-45087077509966067152009-04-28T22:47:00.000-07:002009-04-29T22:53:16.715-07:00ICMBE 2008, Aug. 3~8th, 2008 at University of British Columbia, BC, Canada<script type="text/javascript"><br />var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");<br />document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));<br /></script><br /><script type="text/javascript"><br />try {<br />var pageTracker = _gat._getTracker("UA-8617726-1");<br />pageTracker._trackPageview();<br />} catch(err) {}</script><br /><p class="MsoNormal">This year’s MBE conference focused on the following main topics<b style="">:<o:p></o:p></b></p> <ol style="margin-top: 0in;" start="1" type="1"><li class="MsoNormal" style="">Self-assembled nanostructures: Quantum Dots, Quantum Wires on compound semiconductors and Si/Ge material systems.</li><li class="MsoNormal" style="">Nitrides: Growth mechanisms, rf vs. NH<sub>3</sub> MBE, material qualities and a little bit of electronic and photonic device results.</li><li class="MsoNormal" style="">Photonic devices: QD lasers, diluted nitride long wavelength lasers, quantum cascade lasers, LEDs and photodetectors</li><li class="MsoNormal" style="">III-V MOSFETs</li><li class="MsoNormal" style="">Widegap oxides</li><li class="MsoNormal" style="">Solar cells</li><li class="MsoNormal" style="">Large production scale MBE operations</li><li class="MsoNormal" style="">Growth control: RHEED with rotation and temperature control</li></ol> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Some topics will be discussed below.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><b style="">Multi-D Nanostrucutres:<o:p></o:p></b></p> <p class="MsoNormal"><b style=""><o:p> </o:p></b></p> <p class="MsoNormal">Multi-dimensional nanostructures and devices continue to attract researchers’ interests. The studies range from III-V quantum dot (QD) lasers for telecommunication applications (QD lasers were finally commercialized after being proposed ¼ century ago); to Si/Ge island formation for Si hole mobility enhancement in CMOS applications; to vertical nanowire (whisker) growths on various of semiconductor substrates for practical applications yet to be realized. All these show that crystal growers are enthusiastic about finding a way to improve the lateral pattern control down to nanometer scale.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><b style="">Nitrides:</b></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">There are several interesting papers on growing GaN heterostructures (using MBE of course). In the plenary talk <span style="color:blue;">PL2.2</span> Dr. Skierbiszewski (<st1:placetype st="on">Institute</st1:placetype> of <st1:placename st="on">High Pressure Physics</st1:placename>, <st1:placename st="on">Polish</st1:placename> <st1:placetype st="on">Academy</st1:placetype> of Science, <st1:place st="on"><st1:country-region st="on">Poland</st1:country-region></st1:place>) described how high quality InGaN/GaN QW lasers can be grown using plasma-assisted MBE (PAMBE) with post-growth surface/optical/electrical properties surpass MOCVD-grown counterparts. By using extreme Ga-rich conditions close to the onset of Ga-droplet formation, a two-dimensional growth can happen at relatively low temperature (700~800<sup>o</sup>C, compared to half of GaN melting point of 1050<sup>o</sup>C, which is used by MOCVD growths). The Ga-rich condition produces a metallic Ga adlayer within which the nitrogen adatoms can diffuse with lowered diffusion barrier energies, and therefore grow two-dimensionally. What makes <st1:city st="on">Dr.</st1:city> Skierbiszewski’s talk even more interesting is that in their institute they can grow GaN single crystal substrates with threading dislocation density <>-2, the synthesis happens in Ga solution at 1300-1600<sup>o</sup>C under N<sub>2</sub> pressure of 8-17 kbar ( 1bar ~ 750 Torr ~ 1 atm, that’s why he’s from the Institute of High Pressure Physics). The size of the single crystal GaN is only about 1cm x 1cm but can be sold for 8~10 K USD a piece! I talked to him during the recess and discussed about whether they do GaN HEMT or not. I found out that somehow they rather grow green-blue lasers than GaN HEMTs (Blue/green lasers make more money than GaN HEMT ICs?). BTW, along the same direction I found out that Sumitomo also produces and sells single crystal 2” GaN substrates, but they need NDA if I want to discuss further with them.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">NH<sub>3 </sub>MBE for GaN attracts more and more attention, too. In my opinion (and maybe many other crystal growers’) energetic particles (in this case N<sub>2</sub><sup>*</sup> radicals) coming out of rf-plasma source are not ideal nitrogen source. CNRS/Picogiga group presented several papers (<span style="color:blue;">WB1.6</span>, <span style="color:blue;">THB2.1</span> invited, and <span style="color:blue;">THB2.2</span>) on GaN layers grown by NH<sub>3</sub> MBE on Si(111). Nitrogen source is provided by injecting 100-200 sccm (as opposed to less than 10 sccm of N<sub>2</sub> for normal PAMBE with rf-plasma source) of NH<sub>3</sub> through a leak valve and thermally cracked on substrate. Therefore the growth temperature is ~ 100<sup>o</sup>C higher than PAMBE. Besides the source of nitrogen, the development of III-nitride devices on Si substrate mostly relies on the management of the dislocation density and the residual strain. The CNRS/Picogiga group managed to grow high quality AlGaN/GaN HEMT structures with n<sub>s</sub> ~ 10<sup>13</sup> cm<sup>-2</sup> and μ<sub>n</sub> ~ 2000 cm<sup>2</sup>/V-s (the number is comparable to, if not better than, MOCVD grown ones. As they said, mobility is not an issue for MBE-grown HEMT anymore). The tricks include first nitridizing the Si substrate surface by impinging NH<sub>3</sub> on cleaned hot Si(111) surface to form a very thin layer of single crystal Si<sub>3</sub>N<sub>4</sub>, this will produce a sharp bottom interface; then using an AlN/GaN/AlN 40nm/250nm/250nm stress mitigating layer to reduce/bend the dislocations resulted from the large lattice mismatch between Si(111) and AlN/GaN; finally grow a thick ( >1.5μm ) GaN buffer layer at an optimized temperature at which the dislocations incline and cancel each other (although the dislocation density of grown epi is still in ~ 10<sup>9</sup> cm<sup>-2</sup> range). The AlGaN/GaN active layers are then grown on top of the buffer layer. They also monitored <i style="">in-situ</i> the curvature of the epi and established a relation between wafer bowing vs. epilayer dislocation density. The summary: convex bowing (means the GaN grows compressively strained on the stress mitigating layer) reduces the dislocation density. But there are more subtle interaction between dislocation density, leakage current of the HEMTs, and the donor density of the 2DEG. When dislocation density drops, the 2DEG donor density increases and the HEMT leakage current also increases.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Dislocation reduction and strain engineering are only two of many obstacles that need to be overcome to produce high quality and reliable GaN HEMTs, no matter what crystal growth technique chosen. Crack formation in grown epilayer resulted from thermal expansion coefficient mismatch between Si or SiC substrates and GaN (or even between AlN and GaN) is another issue, for example. Growing HEMTs on single crystal GaN substrates (if they get large enough and cheap enough) could theoretically solve most of the problems, but poor thermal conductivity of GaN (656 mW/cm<sup>-1</sup>K<sup>-1</sup>) compared to 6H-SiC (4900 mW/cm<sup>-1</sup>K<sup>-1</sup>) could potentially hamper its practical use.</p> <p class="MsoNormal"><o:p><br /></o:p></p> <p class="MsoNormal"><b style="">MBE Large-Scale Production and Growth Control:<o:p></o:p></b></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Besides nitrides there are also several papers on MBE growth control and large scale MBE production operation. Tom Rogers of RFMD shared their operation details (<span style="color:blue;">TUA2.1</span>), which can be leveraged by us. Details include:</p> <ol style="margin-top: 0in;" start="1" type="1"><li class="MsoNormal" style="">Minimal number of device structures</li><li class="MsoNormal" style="">Several items can be used as production metrics:</li><ol style="margin-top: 0in;" start="1" type="a"><li class="MsoNormal" style="">System uptime, throughput, and yield</li><li class="MsoNormal" style="">Manpower efficiency</li><li class="MsoNormal" style="">Reproducibility inter MBE systems</li><li class="MsoNormal" style="">Wafer uniformity and run-to-run reproducibility</li></ol><li class="MsoNormal" style="">Documentation, training and uniform methods are critical for multi-shift pass-downs</li><li class="MsoNormal" style="">Using of band-edge <span style=""> </span>thermometry (from kSA) to reduce temperature variation of wafers across a huge platen (7 x 6”, Veeco Gen2000) from 5.78<sup>o</sup>C to 1.5<sup>o</sup>C by optimizing the platen structure (wafer ledge and backing ring wideth), proper coating of platens with semiconductors, and fine-tuning the power ratio and distance between the heater and the platen (<span style="color:blue;">TUA2.3</span>). </li><li class="MsoNormal" style="">Precision MBE system downtime forecasting</li><li class="MsoNormal" style="">24 hr HBT QTA turn-around time</li><li class="MsoNormal" style="">Pareto analysis of reject causes</li><li class="MsoNormal" style="">SEMI-standard definitions and tool states</li></ol> <p class="MsoNormal"><o:p> </o:p></p> For growth control I found out that RHEED oscillation can be done on rotating substrates. It is simple in theory: synchronize the RHEED image capturing with substrate rotation. A rotation speed detection mechanism will be added by the CAR outside the vacuum and triggers the capture of RHEED intensity. In practice there are few concerns such as less available data points and therefore worse fitting; and the annoying wafer skidding. But it proves that RHEED works better than just monitoring <a href="http://engineer-in-wine-country.blogspot.com/2009/04/mbe-native-oxide-desorption.html">substrate oxide desorption</a><a href="http://engineer-in-wine-country.blogspot.com/2009/04/mbe-native-oxide-desorption.html">.</a>MBE guy in wine countryhttp://www.blogger.com/profile/11729854844886575971noreply@blogger.com0