In this study, various surface cleaning techniques for the removal of carbon (C) and oxygen (O) from AlN and GaN were investigated. Auger electron spectroscopy (AES) and secondary mass ion spectroscopy were used to monitor the presence of surface C and O, and atomic force microscopy was used to monitor surface roughness. AES analysis showed that ex situ ultraviolet/ozone (UV/O 3 ) and wet chemical treatments based on HF and HCl were very effective in removing surface C and reducing the native oxide on both AlN and GaN. After H 2 and N 2 plasma treatments in ultrahigh vacuum at temperatures of 750 and 900ЊC, clean GaN surfaces could be achieved within the detection limits of AES. An oxygen-free AlN surface could not be obtained within the detection limits of AES. SIMS analysis showed that concentrations of surface C and O up to 3 ϫ 10 20 and 2 ϫ 10 22 cm Ϫ3 , respectively, still exists on plasma-treated GaN. The results of this study indicate that ex situ UV/O 3 followed by H 2 /N 2 plasma treatment is highly effective in reducing the C and O contamination at the GaN surface, but that further in situ methods are needed to obtain clean GaN and AlN surfaces. None of the various cleaning methods were found to affect the surface roughness.

A GaN/AIGaN heterojunction bipolar transistor structure with Mg doping in the base and Si doping in the emitter and collector regions was grown by Metal Organic Chemical Vapor Deposition on c-axis A1203. Secondary Ion Mass Spectrometry measurements showed no increase in the 0 concentration ( 2 -3~1 0 '~ ~m -~) in the AlGaN emitter and fairly low levels of C (-4-5~10'~ cm-3) throughout the structure. Due to the non-ohmic behavior of the base contact at room temperature, the current gain of large area (-90 pm diameter) devices was <3. Increasing the device operating temperature led to higher ionization fractions of the Mg acceptors in the base, and current gains of -10 were obtained at 300 OC. 1There is a strong interest in GaN-based electronics for applications involving high temperature or high power operation, based on the excellent transport properties of the III-nitride materials system.(*-7' Impressive advances in the performance of AlGaN/GaN high electron mobility transistors continue to be reported, due to in part to the formation of piezoelectrically-induced carriers in a 2-dimensional electron gas at the There is also interest in the development of GaN/AIGaN In this letter we report on the growth by MOCVD of a graded emitter HBT structure, DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document.Spectrometry (SIMS) since these could potentially have a strong influence on device performance, and finally on the dc characteristics of HBTs fabricated on this material.The layer structure is shown schematically in Figure 1, and was grown at -1050 "C following deposition of the GaN buffer at -550 "C on the c-plane A1203 substrate. The growth system has been described in detail previously,'2o' but in brief is a rotating (1200 rpm) disk MOCVD reactor. Ammonia (NH3), trimethylgallium (TMGa) and trimethylaluminum (TMAl) were used as precursors, while silane (SiH4) and biscyclopentadienyl-magnesium (CpzMg) were employed for n-and p-type doping, respectively. High purity H2 was used as the carrier gas. After growth the sample was annealed in the reactor at 850 "C for 20 min under 140 Torr of flowing N2 to activate the Mg acceptors.There are two important aspects to dopant and background impurity control in HBT structures. The first is that the p-type dopant should be confined to the base region, and not spill-over into the adjacent n-type emitter, where it could cause displacement of the junction and hence the loss of the advantage of the heterostructure. Figure 2 shows SIMS profiles of the A1 marker, signifying the position of AlGaN emitter layer, and also the Mg doping profile in the adjacent base layer. It is clear that the reactor memory effect for Cp2Mg has produced incorporation of Mg in the emitter, although the real situation is not quite as severe as it seems in the data because of "carry-over" of the matrix A1 signal during the depth profiling. The fact that working HBTs can still be made on this material is due...

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High-density plasma etching has been an effective patterning technique for the group-III nitrides due to ion fluxes which are two to four orders of magnitude higher than more conventional reactive ion etch systems. GaN etch rates exceeding 0.5 μm/min have been reported in inductively coupled plasma (ICP) etch systems at relatively high dc-biases (&gt;200 V). However, under these conditions, the etch mechanism is dominated by ion bombardment energies which can induce damage and minimize etch selectivity. Development of etch processes with high selectivity has become relevant with recent interest in high power, high temperature electronic devices. In this study, we report ICP etch rates and selectivities for GaN, AlN, and InN in Cl2/Ar, Cl2/N2, Cl2/H2, Cl2/SF6, BCl3/Ar, BCl3/H2, BCl3/N2, and BCl3/SF6 plasma chemistries.

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